diff --git a/README.md b/README.md
index 757e4c58..67183f4d 100644
--- a/README.md
+++ b/README.md
@@ -110,9 +110,9 @@ Monitoring the advertising packets, you can find your devices and know the lates
 
 ```JavaScript
 // Load the node-switchbot and get a `Switchbot` constructor object
-let Switchbot = require('node-switchbot');
+const Switchbot = require('node-switchbot');
 // Create an `Switchbot` object
-let switchbot = new Switchbot();
+const switchbot = new Switchbot();
 
 (async () => {
   // Start to monitor advertisement packets
@@ -137,9 +137,9 @@ The [`startScan()`](#startscan-method) and [`wait()`](#Switchbot-wait-method) me
 
 ```javascript
 // Load the node-switchbot and get a `Switchbot` constructor object
-let Switchbot = require("node-switchbot");
+const Switchbot = require("node-switchbot");
 // Create an `Switchbot` object
-let switchbot = new Switchbot();
+const switchbot = new Switchbot();
 
 // Start to monitor advertisement packets
 switchbot
@@ -213,18 +213,18 @@ This sample discovers a Bot (WoHand), then put the Bot's arm down, finally put i
 
 ```javascript
 // Load the node-switchbot and get a `Switchbot` constructor object
-let Switchbot = require("node-switchbot");
+const Switchbot = require("node-switchbot");
 // Create an `Switchbot` object
-let switchbot = new Switchbot();
+const switchbot = new Switchbot();
 
 (async () => {
   // Find a Bot (WoHand)
-  let bot_list = await switchbot.discover({ model: "H", quick: true });
+  const bot_list = await switchbot.discover({ model: "H", quick: true });
   if (bot_list.length === 0) {
     throw new Error("No device was found.");
   }
   // The `SwitchbotDeviceWoHand` object representing the found Bot.
-  let device = bot_list[0];
+  const device = bot_list[0];
   // Put the Bot's arm down (stretch the arm)
   await device.down();
   // Wait for 5 seconds
@@ -246,13 +246,13 @@ In this code, you can get a [`SwitchbotDeviceWoHand`](#SwitchbotDeviceWoHand-obj
 In order to use the node-switchbot, you have to load the node-switchbot module as follows:
 
 ```JavaScript
-let Switchbot = require('node-switchbot');
+const Switchbot = require('node-switchbot');
 ```
 
 You can get an `Switchbot` constructor from the code above. Then you have to create an `Switchbot` object from the `Switchbot` constructor as follows:
 
 ```javascript
-let switchbot = new Switchbot();
+const switchbot = new Switchbot();
 ```
 
 The `Switchbot` constructor takes an argument optionally. It must be a hash object containing the properties as follows:
@@ -263,15 +263,15 @@ The `Switchbot` constructor takes an argument optionally. It must be a hash obje
 
 The node-switchbot module uses the [`@abandonware/noble`](https://github.com/abandonware/noble) module in order to interact with BLE devices. If you want to interact other BLE devices using the `@abandonware/noble` module, you can create an `Noble` object by yourself, then pass it to this module. If you don't specify a `Noble` object to the `noble` property, this module automatically create a `Noble` object internally.
 
-The sample code below shows how to pass a `Nobel` object to the `Switchbot` constructor.
+The sample code below shows how to pass a `Noble` object to the `Switchbot` constructor.
 
 ```JavaScript
 // Create a Noble object
-let noble = require('@abandonware/noble');
+const noble = require('@abandonware/noble');
 
 // Create a Switchbot object
-let Switchbot = require('node-switchbot');
-let switchbot = new Switchbot({'noble': noble});
+const Switchbot = require('node-switchbot');
+const switchbot = new Switchbot({'noble': noble});
 ```
 
 In the code snippet above, the variable `switchbot` is an `Switchbot` object. The `Switchbot` object has a lot of methods as described in sections below.
@@ -565,7 +565,7 @@ The code below calls the [`press()`](#SwitchbotDeviceWoHand-press-method) method
 switchbot
   .discover({ model: "H", quick: true })
   .then((device_list) => {
-    let device = device_list[0];
+    const device = device_list[0];
     if (!device) {
       console.log("No device was found.");
       process.exit();
diff --git a/lib/parameter-checker.js b/lib/parameter-checker.js
index cbb3f2c6..39a2d5a7 100644
--- a/lib/parameter-checker.js
+++ b/lib/parameter-checker.js
@@ -37,7 +37,7 @@ class ParameterChecker {
    *   an `Error` object will be set to `this._error`.
    *
    * [Usage]
-   * let valid = parameterChecker.check(params, {
+   * const valid = parameterChecker.check(params, {
    *   level: {
    *     required: false,
    *     type: 'integer',
@@ -50,7 +50,7 @@ class ParameterChecker {
    *   }
    * });
    * if(!valid) {
-   *   let e = parameterChecker.error.message;
+   *   const e = parameterChecker.error.message;
    *   throw new Error(message);
    * }
    * ---------------------------------------------------------------- */
@@ -79,11 +79,11 @@ class ParameterChecker {
     }
 
     let result = true;
-    let name_list = Object.keys(rules);
+    const name_list = Object.keys(rules);
 
     for (let i = 0; i < name_list.length; i++) {
-      let name = name_list[i];
-      let v = obj[name];
+      const name = name_list[i];
+      const v = obj[name];
       let rule = rules[name];
 
       if (!rule) {
@@ -458,7 +458,7 @@ class ParameterChecker {
       }
     }
     if (typeof rule.minBytes === "number") {
-      let blen = Buffer.from(value, "utf8").length;
+      const blen = Buffer.from(value, "utf8").length;
       if (blen < rule.minBytes) {
         this._error = {
           code: "LENGTH_UNDERFLOW",
@@ -475,7 +475,7 @@ class ParameterChecker {
       }
     }
     if (typeof rule.maxBytes === "number") {
-      let blen = Buffer.from(value, "utf8").length;
+      const blen = Buffer.from(value, "utf8").length;
       if (blen > rule.maxBytes) {
         this._error = {
           code: "LENGTH_OVERFLOW",
diff --git a/lib/switchbot-advertising.js b/lib/switchbot-advertising.js
index 9d7511ff..ca766ad4 100644
--- a/lib/switchbot-advertising.js
+++ b/lib/switchbot-advertising.js
@@ -61,16 +61,16 @@ class SwitchbotAdvertising {
    * device, this method will return `null`.
    * ---------------------------------------------------------------- */
   parse(peripheral, onlog) {
-    let ad = peripheral.advertisement;
+    const ad = peripheral.advertisement;
     if (!ad || !ad.serviceData) {
       return null;
     }
-    let serviceData = ad.serviceData[0] || ad.serviceData;
-    let manufacturerData = ad.manufacturerData;
-    let buf = serviceData.data;
+    const serviceData = ad.serviceData[0] || ad.serviceData;
+    const manufacturerData = ad.manufacturerData;
+    const buf = serviceData.data;
 
-    let bufIsInvalid = !buf || !Buffer.isBuffer(buf) || buf.length < 3;
-    let manufacturerDataIsInvalid =
+    const bufIsInvalid = !buf || !Buffer.isBuffer(buf) || buf.length < 3;
+    const manufacturerDataIsInvalid =
       !manufacturerData ||
       !Buffer.isBuffer(manufacturerData) ||
       manufacturerData.length < 3;
@@ -79,7 +79,7 @@ class SwitchbotAdvertising {
       return null;
     }
 
-    let model = buf.slice(0, 1).toString("utf8");
+    const model = buf.slice(0, 1).toString("utf8");
     let sd = null;
 
     if (model === "H") {
@@ -129,7 +129,7 @@ class SwitchbotAdvertising {
     if (address === "") {
       address = peripheral.advertisement.manufacturerData || "";
       if (address !== "") {
-        let str = peripheral.advertisement.manufacturerData
+        const str = peripheral.advertisement.manufacturerData
           .toString("hex")
           .slice(4, 16);
         address = str.substr(0, 2);
@@ -141,7 +141,7 @@ class SwitchbotAdvertising {
     } else {
       address = address.replace(/-/g, ":");
     }
-    let data = {
+    const data = {
       id: peripheral.id,
       address: address,
       rssi: peripheral.rssi,
@@ -167,14 +167,14 @@ class SwitchbotAdvertising {
       }
       return null;
     }
-    let byte1 = buf.readUInt8(1);
-    let byte2 = buf.readUInt8(2);
+    const byte1 = buf.readUInt8(1);
+    const byte2 = buf.readUInt8(2);
 
-    let mode = byte1 & 0b10000000 ? true : false; // Whether the light switch Add-on is used or not
-    let state = byte1 & 0b01000000 ? true : false; // Whether the switch status is ON or OFF
-    let battery = byte2 & 0b01111111; // %
+    const mode = byte1 & 0b10000000 ? true : false; // Whether the light switch Add-on is used or not
+    const state = byte1 & 0b01000000 ? true : false; // Whether the switch status is ON or OFF
+    const battery = byte2 & 0b01111111; // %
 
-    let data = {
+    const data = {
       model: "H",
       modelName: "WoHand",
       mode: mode,
@@ -194,17 +194,17 @@ class SwitchbotAdvertising {
       }
       return null;
     }
-    let byte2 = buf.readUInt8(2);
-    let byte3 = buf.readUInt8(3);
-    let byte4 = buf.readUInt8(4);
-    let byte5 = buf.readUInt8(5);
-
-    let temp_sign = byte4 & 0b10000000 ? 1 : -1;
-    let temp_c = temp_sign * ((byte4 & 0b01111111) + (byte3 & 0b00001111) / 10);
-    let temp_f = (temp_c * 9 / 5) + 32;
+    const byte2 = buf.readUInt8(2);
+    const byte3 = buf.readUInt8(3);
+    const byte4 = buf.readUInt8(4);
+    const byte5 = buf.readUInt8(5);
+
+    const temp_sign = byte4 & 0b10000000 ? 1 : -1;
+    const temp_c = temp_sign * ((byte4 & 0b01111111) + (byte3 & 0b00001111) / 10);
+    const temp_f = (temp_c * 9 / 5) + 32;
     temp_f = Math.round(temp_f * 10) / 10;
 
-    let data = {
+    const data = {
       model: "T",
       modelName: "WoSensorTH",
       temperature: {
@@ -228,15 +228,15 @@ class SwitchbotAdvertising {
       }
       return null;
     }
-    let byte1 = buf.readUInt8(1);
-    let byte4 = buf.readUInt8(4);
+    const byte1 = buf.readUInt8(1);
+    const byte4 = buf.readUInt8(4);
     
 
-    let onState = byte1 & 0b10000000 ? true : false; // 1 - on
-    let autoMode = byte4 & 0b10000000 ? true : false; // 1 - auto
-    let percentage = byte4 & 0b01111111; // 0-100%, 101/102/103 - Quick gear 1/2/3
+    const onState = byte1 & 0b10000000 ? true : false; // 1 - on
+    const autoMode = byte4 & 0b10000000 ? true : false; // 1 - auto
+    const percentage = byte4 & 0b01111111; // 0-100%, 101/102/103 - Quick gear 1/2/3
 
-    let data = {
+    const data = {
       model: "e",
       modelName: "WoHumi",
       onState: onState,
@@ -257,20 +257,20 @@ class SwitchbotAdvertising {
       return null;
     }
 
-    let byte1 = buf.readUInt8(1);
-    let byte2 = buf.readUInt8(2);
-    let byte5 = buf.readUInt8(5);
+    const byte1 = buf.readUInt8(1);
+    const byte2 = buf.readUInt8(2);
+    const byte5 = buf.readUInt8(5);
 
-    let tested = byte1 & 0b10000000 ? true : false;
-    let movement = byte1 & 0b01000000 ? true : false;
-    let battery = byte2 & 0b01111111;
-    let led = (byte5 & 0b00100000) >> 5;
-    let iot = (byte5 & 0b00010000) >> 4;
-    let sense_distance = (byte5 & 0b00001100) >> 2;
-    let lightLevel = byte5 & 0b00000011;
-    let is_light = byte5 & 0b00000010 ? true : false;
+    const tested = byte1 & 0b10000000 ? true : false;
+    const movement = byte1 & 0b01000000 ? true : false;
+    const battery = byte2 & 0b01111111;
+    const led = (byte5 & 0b00100000) >> 5;
+    const iot = (byte5 & 0b00010000) >> 4;
+    const sense_distance = (byte5 & 0b00001100) >> 2;
+    const lightLevel = byte5 & 0b00000011;
+    const is_light = byte5 & 0b00000010 ? true : false;
 
-    let data = {
+    const data = {
       model: "s",
       modelName: "WoMotion",
       tested: tested,
@@ -297,21 +297,21 @@ class SwitchbotAdvertising {
       return null;
     }
 
-    let byte1 = buf.readUInt8(1);
-    let byte2 = buf.readUInt8(2);
-    let byte3 = buf.readUInt8(3);
-    let byte8 = buf.readUInt8(8);
-
-    let hallState = (byte3 >> 1) & 0b00000011;
-    let tested = byte1 & 0b10000000;
-    let movement = byte1 & 0b01000000 ? true : false; // 1 - Movement detected
-    let battery = byte2 & 0b01111111; // %
-    let contact_open = byte3 & 0b00000010 == 0b00000010;
-    let contact_timeout = byte3 & 0b00000100 == 0b00000100;
-    let lightLevel = byte3 & 0b00000001;
-    let button_count = byte8 & 0b00001111;
-
-    let data = {
+    const byte1 = buf.readUInt8(1);
+    const byte2 = buf.readUInt8(2);
+    const byte3 = buf.readUInt8(3);
+    const byte8 = buf.readUInt8(8);
+
+    const hallState = (byte3 >> 1) & 0b00000011;
+    const tested = byte1 & 0b10000000;
+    const movement = byte1 & 0b01000000 ? true : false; // 1 - Movement detected
+    const battery = byte2 & 0b01111111; // %
+    const contact_open = byte3 & 0b00000010 == 0b00000010;
+    const contact_timeout = byte3 & 0b00000100 == 0b00000100;
+    const lightLevel = byte3 & 0b00000001;
+    const button_count = byte8 & 0b00001111;
+
+    const data = {
       model: "d",
       modelName: "WoContact",
       movement: movement,
@@ -341,19 +341,19 @@ class SwitchbotAdvertising {
       }
       return null;
     }
-    let byte1 = buf.readUInt8(1);
-    let byte2 = buf.readUInt8(2);
-    let byte3 = buf.readUInt8(3);
-    let byte4 = buf.readUInt8(4);
-
-    let calibration = byte1 & 0b01000000 ? true : false; // Whether the calibration is completed
-    let battery = byte2 & 0b01111111; // %
-    let inMotion = byte3 & 0b10000000 ? true : false;
-    let currPosition = byte3 & 0b01111111; // current positon %
-    let lightLevel = (byte4 >> 4) & 0b00001111; // light sensor level (1-10)
-    let deviceChain = byte4 & 0b00000111;
-
-    let data = {
+    const byte1 = buf.readUInt8(1);
+    const byte2 = buf.readUInt8(2);
+    const byte3 = buf.readUInt8(3);
+    const byte4 = buf.readUInt8(4);
+
+    const calibration = byte1 & 0b01000000 ? true : false; // Whether the calibration is compconsted
+    const battery = byte2 & 0b01111111; // %
+    const inMotion = byte3 & 0b10000000 ? true : false;
+    const currPosition = byte3 & 0b01111111; // current positon %
+    const lightLevel = (byte4 >> 4) & 0b00001111; // light sensor level (1-10)
+    const deviceChain = byte4 & 0b00000111;
+
+    const data = {
       model: "c",
       modelName: "WoCurtain",
       calibration: calibration,
@@ -407,31 +407,31 @@ class SwitchbotAdvertising {
       }
       return null;
     }
-    let byte1 = manufacturerData.readUInt8(1);//power and light status
-    let byte2 = manufacturerData.readUInt8(2);//bulb brightness
-    let byte3 = manufacturerData.readUInt8(3);//bulb R
-    let byte4 = manufacturerData.readUInt8(4);//bulb G
-    let byte5 = manufacturerData.readUInt8(5);//bulb B
-    let byte6 = manufacturerData.readUInt8(6);//bulb temperature
-    let byte7 = manufacturerData.readUInt8(7);
-    let byte8 = manufacturerData.readUInt8(8);
-    let byte9 = manufacturerData.readUInt8(9);
-    let byte10 = manufacturerData.readUInt8(10);//bulb mode
-
-    let power = byte1;
-    let red = byte3;
-    let green = byte4;
-    let blue = byte5;
-    let color_temperature = byte6;
-    let state = byte7 & 0b01111111 ? true : false;
-    let brightness = byte7 & 0b01111111;
-    let delay = byte8 & 0b10000000;
-    let preset = byte8 & 0b00001000;
-    let color_mode = byte8 & 0b00000111;
-    let speed = byte9 & 0b01111111;
-    let loop_index = byte10 & 0b11111110;
-
-    let data = {
+    const byte1 = manufacturerData.readUInt8(1);//power and light status
+    const byte2 = manufacturerData.readUInt8(2);//bulb brightness
+    const byte3 = manufacturerData.readUInt8(3);//bulb R
+    const byte4 = manufacturerData.readUInt8(4);//bulb G
+    const byte5 = manufacturerData.readUInt8(5);//bulb B
+    const byte6 = manufacturerData.readUInt8(6);//bulb temperature
+    const byte7 = manufacturerData.readUInt8(7);
+    const byte8 = manufacturerData.readUInt8(8);
+    const byte9 = manufacturerData.readUInt8(9);
+    const byte10 = manufacturerData.readUInt8(10);//bulb mode
+
+    const power = byte1;
+    const red = byte3;
+    const green = byte4;
+    const blue = byte5;
+    const color_temperature = byte6;
+    const state = byte7 & 0b01111111 ? true : false;
+    const brightness = byte7 & 0b01111111;
+    const delay = byte8 & 0b10000000;
+    const preset = byte8 & 0b00001000;
+    const color_mode = byte8 & 0b00000111;
+    const speed = byte9 & 0b01111111;
+    const loop_index = byte10 & 0b11111110;
+
+    const data = {
       model: "u",
       modelName: "WoBulb",
       color_temperature: color_temperature,
@@ -460,22 +460,22 @@ class SwitchbotAdvertising {
       }
       return null;
     }
-    let byte9 = manufacturerData.readUInt8(9); // byte9:  plug mini state; 0x00=off, 0x80=on
-    let byte10 = manufacturerData.readUInt8(10); // byte10: bit0: 0=no delay,1=delay, bit1:0=no timer, 1=timer; bit2:0=no sync time, 1=sync'ed time
-    let byte11 = manufacturerData.readUInt8(11); // byte11: wifi rssi
-    let byte12 = manufacturerData.readUInt8(12); // byte12: bit7: overload?
-    let byte13 = manufacturerData.readUInt8(13); // byte12[bit0~6] + byte13: current power value
-
-    let state = byte9 === 0x00 ? "off" : byte9 === 0x80 ? "on" : null;
-    let delay = !!(byte10 & 0b00000001);
-    let timer = !!(byte10 & 0b00000010);
-    let syncUtcTime = !!(byte10 & 0b00000100);
-    let wifiRssi = byte11;
-    let overload = !!(byte12 & 0b10000000);
-    let currentPower = (((byte12 & 0b01111111) << 8) + byte13) / 10; // in watt
+    const byte9 = manufacturerData.readUInt8(9); // byte9:  plug mini state; 0x00=off, 0x80=on
+    const byte10 = manufacturerData.readUInt8(10); // byte10: bit0: 0=no delay,1=delay, bit1:0=no timer, 1=timer; bit2:0=no sync time, 1=sync'ed time
+    const byte11 = manufacturerData.readUInt8(11); // byte11: wifi rssi
+    const byte12 = manufacturerData.readUInt8(12); // byte12: bit7: overload?
+    const byte13 = manufacturerData.readUInt8(13); // byte12[bit0~6] + byte13: current power value
+
+    const state = byte9 === 0x00 ? "off" : byte9 === 0x80 ? "on" : null;
+    const delay = !!(byte10 & 0b00000001);
+    const timer = !!(byte10 & 0b00000010);
+    const syncUtcTime = !!(byte10 & 0b00000100);
+    const wifiRssi = byte11;
+    const overload = !!(byte12 & 0b10000000);
+    const currentPower = (((byte12 & 0b01111111) << 8) + byte13) / 10; // in watt
     // TODO: voltage ???
 
-    let data = {
+    const data = {
       model: "g",
       modelName: "WoPlugMini",
       state: state,
@@ -499,22 +499,22 @@ class SwitchbotAdvertising {
       }
       return null;
     }
-    let byte9 = manufacturerData.readUInt8(9); // byte9:  plug mini state; 0x00=off, 0x80=on
-    let byte10 = manufacturerData.readUInt8(10); // byte10: bit0: 0=no delay,1=delay, bit1:0=no timer, 1=timer; bit2:0=no sync time, 1=sync'ed time
-    let byte11 = manufacturerData.readUInt8(11); // byte11: wifi rssi
-    let byte12 = manufacturerData.readUInt8(12); // byte12: bit7: overload?
-    let byte13 = manufacturerData.readUInt8(13); // byte12[bit0~6] + byte13: current power value
-
-    let state = byte9 === 0x00 ? "off" : byte9 === 0x80 ? "on" : null;
-    let delay = !!(byte10 & 0b00000001);
-    let timer = !!(byte10 & 0b00000010);
-    let syncUtcTime = !!(byte10 & 0b00000100);
-    let wifiRssi = byte11;
-    let overload = !!(byte12 & 0b10000000);
-    let currentPower = (((byte12 & 0b01111111) << 8) + byte13) / 10; // in watt
+    const byte9 = manufacturerData.readUInt8(9); // byte9:  plug mini state; 0x00=off, 0x80=on
+    const byte10 = manufacturerData.readUInt8(10); // byte10: bit0: 0=no delay,1=delay, bit1:0=no timer, 1=timer; bit2:0=no sync time, 1=sync'ed time
+    const byte11 = manufacturerData.readUInt8(11); // byte11: wifi rssi
+    const byte12 = manufacturerData.readUInt8(12); // byte12: bit7: overload?
+    const byte13 = manufacturerData.readUInt8(13); // byte12[bit0~6] + byte13: current power value
+
+    const state = byte9 === 0x00 ? "off" : byte9 === 0x80 ? "on" : null;
+    const delay = !!(byte10 & 0b00000001);
+    const timer = !!(byte10 & 0b00000010);
+    const syncUtcTime = !!(byte10 & 0b00000100);
+    const wifiRssi = byte11;
+    const overload = !!(byte12 & 0b10000000);
+    const currentPower = (((byte12 & 0b01111111) << 8) + byte13) / 10; // in watt
     // TODO: voltage ???
 
-    let data = {
+    const data = {
       model: "j",
       modelName: "WoPlugMini",
       state: state,
@@ -538,12 +538,12 @@ class SwitchbotAdvertising {
       }
       return null;
     }
-    let byte2 = manufacturerData.readUInt8(2);
-    let byte7 = manufacturerData.readUInt8(7);
-    let byte8 = manufacturerData.readUInt8(8);
+    const byte2 = manufacturerData.readUInt8(2);
+    const byte7 = manufacturerData.readUInt8(7);
+    const byte8 = manufacturerData.readUInt8(8);
 
     
-    let LockStatus = {
+    const LockStatus = {
       LOCKED: 0b0000000,
       UNLOCKED: 0b0010000,
       LOCKING: 0b0100000,
@@ -553,17 +553,17 @@ class SwitchbotAdvertising {
       NOT_FULLY_LOCKED: 0b1100000,  //Only EU lock type
      }
 
-    let battery = byte2 & 0b01111111; // %
-    let calibration = byte7 & 0b10000000 ? true : false;
-    let status = LockStatus(byte7 & 0b01110000);
-    let update_from_secondary_lock = byte7 & 0b00001000 ? true : false;
-    let door_open = byte7 & 0b00000100 ? true : false;
-    let double_lock_mode = byte8 & 0b10000000 ? true : false;
-    let unclosed_alarm = byte8 & 0b00100000 ? true : false;
-    let unlocked_alarm = byte8 & 0b00010000 ? true : false;
-    let auto_lock_paused = byte8 & 0b00000010 ? true : false;
-
-    let data = {
+    const battery = byte2 & 0b01111111; // %
+    const calibration = byte7 & 0b10000000 ? true : false;
+    const status = LockStatus(byte7 & 0b01110000);
+    const update_from_secondary_lock = byte7 & 0b00001000 ? true : false;
+    const door_open = byte7 & 0b00000100 ? true : false;
+    const double_lock_mode = byte8 & 0b10000000 ? true : false;
+    const unclosed_alarm = byte8 & 0b00100000 ? true : false;
+    const unlocked_alarm = byte8 & 0b00010000 ? true : false;
+    const auto_lock_paused = byte8 & 0b00000010 ? true : false;
+
+    const data = {
       model: "o",
       modelName: "WoSmartLock",
       battery: battery,
@@ -589,17 +589,17 @@ class SwitchbotAdvertising {
       }
       return null;
     }
-    let byte2 = buf.readUInt8(2);
-    let byte3 = buf.readUInt8(3);
-    let byte4 = buf.readUInt8(4);
-    let byte5 = buf.readUInt8(5);
-
-    let temp_sign = byte4 & 0b10000000 ? 1 : -1;
-    let temp_c = temp_sign * ((byte4 & 0b01111111) + (byte3 & 0b00001111) / 10);
-    let temp_f = (temp_c * 9 / 5) + 32;
+    const byte2 = buf.readUInt8(2);
+    const byte3 = buf.readUInt8(3);
+    const byte4 = buf.readUInt8(4);
+    const byte5 = buf.readUInt8(5);
+
+    const temp_sign = byte4 & 0b10000000 ? 1 : -1;
+    const temp_c = temp_sign * ((byte4 & 0b01111111) + (byte3 & 0b00001111) / 10);
+    const temp_f = (temp_c * 9 / 5) + 32;
     temp_f = Math.round(temp_f * 10) / 10;
 
-    let data = {
+    const data = {
       model: "i",
       modelName: "WoSensorTHPlus",
       temperature: {
@@ -624,28 +624,28 @@ class SwitchbotAdvertising {
       return null;
     }
 
-    let byte1 = buf.readUInt8(1);//power and light status
-    let byte2 = buf.readUInt8(2);//bulb brightness
-    let byte3 = buf.readUInt8(3);//bulb R
-    let byte4 = buf.readUInt8(4);//bulb G
-    let byte5 = buf.readUInt8(5);//bulb B
-    let byte7 = buf.readUInt8(7);
-    let byte8 = buf.readUInt8(8);
-    let byte9 = buf.readUInt8(9);
-    let byte10 = buf.readUInt8(10);
-
-    let state = byte7 & 0b10000000 ? true : false;
-    let brightness = byte7 & 0b01111111;
-    let red = byte3;
-    let green = byte4;
-    let blue = byte5;
-    let delay = byte8 & 0b10000000;
-    let preset = byte8 & 0b00001000;
-    let color_mode = byte8 & 0b00000111;
-    let speed = byte9 & 0b01111111;
-    let loop_index = byte10 & 0b11111110;
-
-    let data = {
+    const byte1 = buf.readUInt8(1);//power and light status
+    const byte2 = buf.readUInt8(2);//bulb brightness
+    const byte3 = buf.readUInt8(3);//bulb R
+    const byte4 = buf.readUInt8(4);//bulb G
+    const byte5 = buf.readUInt8(5);//bulb B
+    const byte7 = buf.readUInt8(7);
+    const byte8 = buf.readUInt8(8);
+    const byte9 = buf.readUInt8(9);
+    const byte10 = buf.readUInt8(10);
+
+    const state = byte7 & 0b10000000 ? true : false;
+    const brightness = byte7 & 0b01111111;
+    const red = byte3;
+    const green = byte4;
+    const blue = byte5;
+    const delay = byte8 & 0b10000000;
+    const preset = byte8 & 0b00001000;
+    const color_mode = byte8 & 0b00000111;
+    const speed = byte9 & 0b01111111;
+    const loop_index = byte10 & 0b11111110;
+
+    const data = {
       model: "r",
       modelName: "WoStrip",
       state: state,
diff --git a/lib/switchbot-device-wobulb.js b/lib/switchbot-device-wobulb.js
index 3146709c..cb0e2a7e 100644
--- a/lib/switchbot-device-wobulb.js
+++ b/lib/switchbot-device-wobulb.js
@@ -1,5 +1,5 @@
 "use strict";
-let SwitchbotDevice = require("./switchbot-device.js");
+const SwitchbotDevice = require("./switchbot-device.js");
 
 /**
  * @see https://github.com/OpenWonderLabs/SwitchBotAPI-BLE/blob/latest/devicetypes/colorbulb.md
@@ -16,7 +16,7 @@ class SwitchbotDeviceWoBulb extends SwitchbotDevice {
    * @private
    */
   _setState(reqByteArray) {
-    let base = [0x57, 0x0f, 0x47, 0x01];
+    const base = [0x57, 0x0f, 0x47, 0x01];
     return this._operateBot([].concat(base, reqByteArray));
   }
 
@@ -149,15 +149,15 @@ class SwitchbotDeviceWoBulb extends SwitchbotDevice {
    * @private
    */
   _operateBot(bytes) {
-    let req_buf = Buffer.from(bytes);
+    const req_buf = Buffer.from(bytes);
     return new Promise((resolve, reject) => {
       this._command(req_buf)
         .then((res_bytes) => {
-          let res_buf = Buffer.from(res_bytes);
+          const res_buf = Buffer.from(res_bytes);
           if (res_buf.length === 2) {
-            let code = res_buf.readUInt8(1);
+            const code = res_buf.readUInt8(1);
             if (code === 0x00 || code === 0x80) {
-              let is_on = code === 0x80;
+              const is_on = code === 0x80;
               resolve(is_on);
             } else {
               reject(
diff --git a/lib/switchbot-device-wocontact.js b/lib/switchbot-device-wocontact.js
index 287959ae..63443786 100644
--- a/lib/switchbot-device-wocontact.js
+++ b/lib/switchbot-device-wocontact.js
@@ -1,5 +1,5 @@
 "use strict";
-let SwitchbotDevice = require("./switchbot-device.js");
+const SwitchbotDevice = require("./switchbot-device.js");
 
 class SwitchbotDeviceWoContact extends SwitchbotDevice {}
 
diff --git a/lib/switchbot-device-wocurtain.js b/lib/switchbot-device-wocurtain.js
index 84200a51..90da249d 100644
--- a/lib/switchbot-device-wocurtain.js
+++ b/lib/switchbot-device-wocurtain.js
@@ -1,5 +1,5 @@
 "use strict";
-let SwitchbotDevice = require("./switchbot-device.js");
+const SwitchbotDevice = require("./switchbot-device.js");
 
 class SwitchbotDeviceWoCurtain extends SwitchbotDevice {
   /* ------------------------------------------------------------------
@@ -93,10 +93,10 @@ class SwitchbotDeviceWoCurtain extends SwitchbotDevice {
 
   _operateCurtain(bytes) {
     return new Promise((resolve, reject) => {
-      let req_buf = Buffer.from(bytes);
+      const req_buf = Buffer.from(bytes);
       this._command(req_buf)
         .then((res_buf) => {
-          let code = res_buf.readUInt8(0);
+          const code = res_buf.readUInt8(0);
           if (res_buf.length === 3 && code === 0x01) {
             resolve();
           } else {
diff --git a/lib/switchbot-device-wohand.js b/lib/switchbot-device-wohand.js
index 891da386..3cd9378f 100644
--- a/lib/switchbot-device-wohand.js
+++ b/lib/switchbot-device-wohand.js
@@ -1,5 +1,5 @@
 "use strict";
-let SwitchbotDevice = require("./switchbot-device.js");
+const SwitchbotDevice = require("./switchbot-device.js");
 
 class SwitchbotDeviceWoHand extends SwitchbotDevice {
   /* ------------------------------------------------------------------
@@ -79,10 +79,10 @@ class SwitchbotDeviceWoHand extends SwitchbotDevice {
 
   _operateBot(bytes) {
     return new Promise((resolve, reject) => {
-      let req_buf = Buffer.from(bytes);
+      const req_buf = Buffer.from(bytes);
       this._command(req_buf)
         .then((res_buf) => {
-          let code = res_buf.readUInt8(0);
+          const code = res_buf.readUInt8(0);
           if (res_buf.length === 3 && (code === 0x01 || code === 0x05)) {
             resolve();
           } else {
diff --git a/lib/switchbot-device-wohumi.js b/lib/switchbot-device-wohumi.js
index 82c8d3e9..e7d055bd 100644
--- a/lib/switchbot-device-wohumi.js
+++ b/lib/switchbot-device-wohumi.js
@@ -1,5 +1,5 @@
 "use strict";
-let SwitchbotDevice = require("./switchbot-device.js");
+const SwitchbotDevice = require("./switchbot-device.js");
 
 class SwitchbotDeviceWoHumi extends SwitchbotDevice {
   /* ------------------------------------------------------------------
@@ -79,10 +79,10 @@ class SwitchbotDeviceWoHumi extends SwitchbotDevice {
 
   _operateBot(bytes) {
     return new Promise((resolve, reject) => {
-      let req_buf = Buffer.from(bytes);
+      const req_buf = Buffer.from(bytes);
       this._command(req_buf)
         .then((res_buf) => {
-          let code = res_buf.readUInt8(0);
+          const code = res_buf.readUInt8(0);
           if (res_buf.length === 3 && (code === 0x01 || code === 0x05)) {
             resolve();
           } else {
diff --git a/lib/switchbot-device-woplugmini.js b/lib/switchbot-device-woplugmini.js
index f156c24a..0e91068d 100644
--- a/lib/switchbot-device-woplugmini.js
+++ b/lib/switchbot-device-woplugmini.js
@@ -1,5 +1,5 @@
 "use strict";
-let SwitchbotDevice = require("./switchbot-device.js");
+const SwitchbotDevice = require("./switchbot-device.js");
 
 /**
  * @see https://github.com/OpenWonderLabs/SwitchBotAPI-BLE/blob/latest/devicetypes/plugmini.md
@@ -16,7 +16,7 @@ class SwitchbotDeviceWoPlugMini extends SwitchbotDevice {
    * @private
    */
   _setState(reqByteArray) {
-    let base = [0x57, 0x0f, 0x50, 0x01];
+    const base = [0x57, 0x0f, 0x50, 0x01];
     return this._operateBot([].concat(base, reqByteArray));
   }
 
@@ -45,15 +45,15 @@ class SwitchbotDeviceWoPlugMini extends SwitchbotDevice {
    * @private
    */
   _operateBot(bytes) {
-    let req_buf = Buffer.from(bytes);
+    const req_buf = Buffer.from(bytes);
     return new Promise((resolve, reject) => {
       this._command(req_buf)
         .then((res_bytes) => {
-          let res_buf = Buffer.from(res_bytes);
+          const res_buf = Buffer.from(res_bytes);
           if (res_buf.length === 2) {
-            let code = res_buf.readUInt8(1);
+            const code = res_buf.readUInt8(1);
             if (code === 0x00 || code === 0x80) {
-              let is_on = code === 0x80;
+              const is_on = code === 0x80;
               resolve(is_on);
             } else {
               reject(
diff --git a/lib/switchbot-device-wopresence.js b/lib/switchbot-device-wopresence.js
index f0cd5779..e5f28ca9 100644
--- a/lib/switchbot-device-wopresence.js
+++ b/lib/switchbot-device-wopresence.js
@@ -1,5 +1,5 @@
 "use strict";
-let SwitchbotDevice = require("./switchbot-device.js");
+const SwitchbotDevice = require("./switchbot-device.js");
 
 class SwitchbotDeviceWoPresence extends SwitchbotDevice {}
 
diff --git a/lib/switchbot-device-wosensorth.js b/lib/switchbot-device-wosensorth.js
index 340b42f5..8f0579a5 100644
--- a/lib/switchbot-device-wosensorth.js
+++ b/lib/switchbot-device-wosensorth.js
@@ -1,5 +1,5 @@
 "use strict";
-let SwitchbotDevice = require("./switchbot-device.js");
+const SwitchbotDevice = require("./switchbot-device.js");
 
 class SwitchbotDeviceWoSensorTH extends SwitchbotDevice {}
 
diff --git a/lib/switchbot-device-wostrip.js b/lib/switchbot-device-wostrip.js
index 37516788..db444e61 100644
--- a/lib/switchbot-device-wostrip.js
+++ b/lib/switchbot-device-wostrip.js
@@ -1,5 +1,5 @@
 "use strict";
-let SwitchbotDevice = require("./switchbot-device.js");
+const SwitchbotDevice = require("./switchbot-device.js");
 
 /**
  * @see https://github.com/OpenWonderLabs/SwitchBotAPI-BLE/blob/latest/devicetypes/colorbulb.md
@@ -16,7 +16,7 @@ class SwitchbotDeviceWoStrip extends SwitchbotDevice {
    * @private
    */
   _setState(reqByteArray) {
-    let base = [0x57, 0x0f, 0x49, 0x01];
+    const base = [0x57, 0x0f, 0x49, 0x01];
     return this._operateBot([].concat(base, reqByteArray));
   }
 
@@ -143,15 +143,15 @@ class SwitchbotDeviceWoStrip extends SwitchbotDevice {
    * @private
    */
   _operateBot(bytes) {
-    let req_buf = Buffer.from(bytes);
+    const req_buf = Buffer.from(bytes);
     return new Promise((resolve, reject) => {
       this._command(req_buf)
         .then((res_bytes) => {
-          let res_buf = Buffer.from(res_bytes);
+          const res_buf = Buffer.from(res_bytes);
           if (res_buf.length === 2) {
-            let code = res_buf.readUInt8(1);
+            const code = res_buf.readUInt8(1);
             if (code === 0x00 || code === 0x80) {
-              let is_on = code === 0x80;
+              const is_on = code === 0x80;
               resolve(is_on);
             } else {
               reject(
diff --git a/lib/switchbot-device.js b/lib/switchbot-device.js
index afa185fa..b1ddaa8c 100644
--- a/lib/switchbot-device.js
+++ b/lib/switchbot-device.js
@@ -1,6 +1,6 @@
 "use strict";
-let parameterChecker = require("./parameter-checker.js");
-let switchbotAdvertising = require("./switchbot-advertising.js");
+const parameterChecker = require("./parameter-checker.js");
+const switchbotAdvertising = require("./switchbot-advertising.js");
 
 class SwitchbotDevice {
   /* ------------------------------------------------------------------
@@ -9,7 +9,7 @@ class SwitchbotDevice {
    * [Arguments]
    * - peripheral | Object | Required | The `peripheral` object of noble,
    *              |        |          | which represents this device
-   * - noble      | Noble  | Required | The Nobel object created by the noble module.
+   * - noble      | Noble  | Required | The Noble object created by the noble module.
    * ---------------------------------------------------------------- */
   constructor(peripheral, noble) {
     this._peripheral = peripheral;
@@ -26,7 +26,7 @@ class SwitchbotDevice {
     this._COMMAND_TIMEOUT_MSEC = 3000;
 
     // Save the device information
-    let ad = switchbotAdvertising.parse(peripheral);
+    const ad = switchbotAdvertising.parse(peripheral);
     this._id = ad.id;
     this._address = ad.address;
     this._model = ad.serviceData.model;
@@ -105,7 +105,7 @@ class SwitchbotDevice {
       }
 
       // Check the connection state
-      let state = this.connectionState;
+      const state = this.connectionState;
       if (state === "connected") {
         resolve();
         return;
@@ -179,19 +179,19 @@ class SwitchbotDevice {
 
       // Discover services and characteristics
       (async () => {
-        let service_list = await this._discoverServices();
+        const service_list = await this._discoverServices();
         if (!timer) {
           throw new Error("");
         }
 
-        let chars = {
+        const chars = {
           write: null,
           notify: null,
           device: null,
         };
 
         for (let service of service_list) {
-          let char_list = await this._discoverCharacteristics(service);
+          const char_list = await this._discoverCharacteristics(service);
           for (let char of char_list) {
             if (char.uuid === this._CHAR_UUID_WRITE) {
               chars.write = char;
@@ -260,7 +260,7 @@ class SwitchbotDevice {
 
   _subscribe() {
     return new Promise((resolve, reject) => {
-      let char = this._chars.notify;
+      const char = this._chars.notify;
       if (!char) {
         reject(new Error("No notify characteristic was found."));
         return;
@@ -280,7 +280,7 @@ class SwitchbotDevice {
 
   _unsubscribe() {
     return new Promise((resolve) => {
-      let char = this._chars.notify;
+      const char = this._chars.notify;
       if (!char) {
         resolve();
         return;
@@ -307,7 +307,7 @@ class SwitchbotDevice {
     return new Promise((resolve, reject) => {
       this._was_connected_explicitly = false;
       // Check the connection state
-      let state = this._peripheral.state;
+      const state = this._peripheral.state;
       if (state === "disconnected") {
         resolve();
         return;
@@ -351,7 +351,7 @@ class SwitchbotDevice {
    * ---------------------------------------------------------------- */
   getDeviceName() {
     return new Promise((resolve, reject) => {
-      let name = "";
+      const name = "";
       this._connect()
         .then(() => {
           if (!this._chars.device) {
@@ -392,7 +392,7 @@ class SwitchbotDevice {
   setDeviceName(name) {
     return new Promise((resolve, reject) => {
       // Check the parameters
-      let valid = parameterChecker.check(
+      const valid = parameterChecker.check(
         { name: name },
         {
           name: { required: true, type: "string", minBytes: 1, maxBytes: 100 },
@@ -404,7 +404,7 @@ class SwitchbotDevice {
         return;
       }
 
-      let buf = Buffer.from(name, "utf8");
+      const buf = Buffer.from(name, "utf8");
       this._connect()
         .then(() => {
           if (!this._chars.device) {
diff --git a/lib/switchbot.js b/lib/switchbot.js
index 362553c2..93557361 100644
--- a/lib/switchbot.js
+++ b/lib/switchbot.js
@@ -1,18 +1,18 @@
 "use strict";
-let parameterChecker = require("./parameter-checker.js");
-let switchbotAdvertising = require("./switchbot-advertising.js");
+const parameterChecker = require("./parameter-checker.js");
+const switchbotAdvertising = require("./switchbot-advertising.js");
 
-let SwitchbotDevice = require("./switchbot-device.js");
-let SwitchbotDeviceWoHand = require("./switchbot-device-wohand.js");
-let SwitchbotDeviceWoCurtain = require("./switchbot-device-wocurtain.js");
-let SwitchbotDeviceWoBlindTilt = require("./switchbot-device-woblindtilt.js");
-let SwitchbotDeviceWoPresence = require("./switchbot-device-wopresence.js");
-let SwitchbotDeviceWoContact = require("./switchbot-device-wocontact.js");
-let SwitchbotDeviceWoSensorTH = require("./switchbot-device-wosensorth.js");
-let SwitchbotDeviceWoHumi = require("./switchbot-device-wohumi.js");
-let SwitchbotDeviceWoPlugMini = require("./switchbot-device-woplugmini.js");
-let SwitchbotDeviceWoBulb = require("./switchbot-device-wobulb.js");
-let SwitchbotDeviceWoStrip = require("./switchbot-device-wostrip.js");
+const SwitchbotDevice = require("./switchbot-device.js");
+const SwitchbotDeviceWoHand = require("./switchbot-device-wohand.js");
+const SwitchbotDeviceWoCurtain = require("./switchbot-device-wocurtain.js");
+const SwitchbotDeviceWoBlindTilt = require("./switchbot-device-woblindtilt.js");
+const SwitchbotDeviceWoPresence = require("./switchbot-device-wopresence.js");
+const SwitchbotDeviceWoContact = require("./switchbot-device-wocontact.js");
+const SwitchbotDeviceWoSensorTH = require("./switchbot-device-wosensorth.js");
+const SwitchbotDeviceWoHumi = require("./switchbot-device-wohumi.js");
+const SwitchbotDeviceWoPlugMini = require("./switchbot-device-woplugmini.js");
+const SwitchbotDeviceWoBulb = require("./switchbot-device-wobulb.js");
+const SwitchbotDeviceWoStrip = require("./switchbot-device-wostrip.js");
 
 class Switchbot {
   /* ------------------------------------------------------------------
@@ -20,7 +20,7 @@ class Switchbot {
    *
    * [Arguments]
    * - params  | Object  | Optional |
-   *   - noble | Noble   | Optional | The Nobel object created by the noble module.
+   *   - noble | Noble   | Optional | The Noble object created by the noble module.
    *           |         |          | This parameter is optional.
    *           |         |          | If you don't specify this parameter, this
    *           |         |          | module automatically creates it.
@@ -84,9 +84,9 @@ class Switchbot {
    *   `SwitchbotDevice` objects representing the found devices.
    * ---------------------------------------------------------------- */
   discover(params = {}) {
-    let promise = new Promise((resolve, reject) => {
+    const promise = new Promise((resolve, reject) => {
       // Check the parameters
-      let valid = parameterChecker.check(
+      const valid = parameterChecker.check(
         params,
         {
           duration: { required: false, type: "integer", min: 1, max: 60000 },
@@ -125,7 +125,7 @@ class Switchbot {
       }
 
       // Determine the values of the parameters
-      let p = {
+      const p = {
         duration: params.duration || this._DEFAULT_DISCOVERY_DURATION,
         model: params.model || "",
         id: params.id || "",
@@ -137,7 +137,7 @@ class Switchbot {
         .then(() => {
           let peripherals = {};
           let timer = null;
-          let finishDiscovery = () => {
+          const finishDiscovery = () => {
             if (timer) {
               clearTimeout(timer);
             }
@@ -154,11 +154,11 @@ class Switchbot {
 
           // Set a handler for the 'discover' event
           this.noble.on("discover", (peripheral) => {
-            let device = this._getDeviceObject(peripheral, p.id, p.model);
+            const device = this._getDeviceObject(peripheral, p.id, p.model);
             if (!device) {
               return;
             }
-            let id = device.id;
+            const id = device.id;
             peripherals[id] = device;
 
             if (this.ondiscover && typeof this.ondiscover === "function") {
@@ -194,13 +194,13 @@ class Switchbot {
   }
 
   _init() {
-    let promise = new Promise((resolve, reject) => {
+    const promise = new Promise((resolve, reject) => {
       switch (this.noble.state) {
         case "poweredOn":
           resolve();
           return;
         case ("unsupported", "unauthorized", "poweredOff"):
-          let err = new Error(
+          const err = new Error(
             "Failed to initialize the Noble object: " + this.noble.state
           );
           reject(err);
@@ -212,7 +212,7 @@ class Switchbot {
             if (state === "poweredOn") {
               resolve();
             } else {
-              let err = new Error(
+              const err = new Error(
                 "Failed to initialize the Noble object: " + state
               );
               reject(err);
@@ -224,7 +224,7 @@ class Switchbot {
   }
 
   _getDeviceObject(peripheral, id, model) {
-    let ad = switchbotAdvertising.parse(peripheral, this.onlog);
+    const ad = switchbotAdvertising.parse(peripheral, this.onlog);
     if (this._filterAdvertising(ad, id, model)) {
       let device = null;
       switch (ad.serviceData.model) {
@@ -280,7 +280,7 @@ class Switchbot {
     }
     if (id) {
       id = id.toLowerCase().replace(/\:/g, "");
-      let ad_id = ad.address.toLowerCase().replace(/[^a-z0-9]/g, "");
+      const ad_id = ad.address.toLowerCase().replace(/[^a-z0-9]/g, "");
       if (ad_id !== id) {
         return false;
       }
@@ -349,9 +349,9 @@ class Switchbot {
    *   Nothing will be passed to the `resolve()`.
    * ---------------------------------------------------------------- */
   startScan(params) {
-    let promise = new Promise((resolve, reject) => {
+    const promise = new Promise((resolve, reject) => {
       // Check the parameters
-      let valid = parameterChecker.check(
+      const valid = parameterChecker.check(
         params,
         {
           model: {
@@ -392,14 +392,14 @@ class Switchbot {
       this._init()
         .then(() => {
           // Determine the values of the parameters
-          let p = {
+          const p = {
             model: params.model || "",
             id: params.id || "",
           };
 
           // Set a handler for the 'discover' event
           this.noble.on("discover", (peripheral) => {
-            let ad = switchbotAdvertising.parse(peripheral, this.onlog);
+            const ad = switchbotAdvertising.parse(peripheral, this.onlog);
             if (this._filterAdvertising(ad, p.id, p.model)) {
               if (
                 this.onadvertisement &&
@@ -459,7 +459,7 @@ class Switchbot {
   wait(msec) {
     return new Promise((resolve, reject) => {
       // Check the parameters
-      let valid = parameterChecker.check(
+      const valid = parameterChecker.check(
         { msec: msec },
         {
           msec: { required: true, type: "integer", min: 0 },