Js concepts

Author: Imam Hossain Santho

1-json.js

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+const fs = require('fs')
+
+const book = {
+    name: 'Imam Hossain',
+    year: 2014
+}
+// const bookJSON = JSON.stringify(book);
+// console.log(bookJSON);
+// fs.writeFileSync('./1-json.json', bookJSON);
+// const bookData = JSON.parse(bookJSON);
+// console.log(bookData); 
+let dataJSON = fs.readFileSync('1-json.json').toString()
+const user = JSON.parse(dataJSON);
+user.year = 1996;
+
+const userJSON  = JSON.stringify(user);
+console.log(userJSON);
+fs.writeFileSync('./1-json.json', userJSON);

2.arrow functions.js

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+const button = document.createElement("button")
+button.textContent = "Click me"
+document.body.append(button)
+
+class Display {
+  constructor() {
+    this.buttonText = "New text"
+
+    button.addEventListener("click", (event) => {
+      event.target.textContent = this.buttonText //this context refers to outher this.buttonText
+    })
+  }
+}
+
+new Display() //New Text Display
+//without arrow function, it will be "click me"

3.iife.js

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+let taskArr = (() => {
+  let arr = []
+  for (let i = 1; i <= 5; i++) {
+    arr.push({
+      name: "Task-1" + i,
+      completed: i % 2 === 0,
+    })
+  }
+  return arr
+})()
+
+console.log(taskArr)

4-callbacks.js

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+/* const geocode = (address, callback) => {
+    return setTimeout(() => {
+        const data = {
+            latitude: 0,
+            longitude: 0
+        }
+        callback(address, data)
+    }, 2000)
+}
+function getData(address, data){
+    console.log(address, ':\n' ,  data);
+}
+geocode('Philadelpia', getData) */
+
+/*******calllback */
+/* add(1, 2, sum)
+function add(a, b, sum) {
+    sum(a+b)
+}
+function sum(result) {
+    console.log(result)
+} */
+/*****closure */
+/* function mul(a, b) {
+    return function mulCallback(c) {
+      console.log(a * b * c)
+    }
+}
+let x = mul(1, 2)
+
+
+console.log(x)
+x(5)
+ */
+
+/*****Callback again */
+
+const doRocketLaunch = (weather, callbackResult) => {
+    setTimeout(function checkingWeather() {
+        if (weather == 'Good') callbackResult(undefined, 'Mission Success!')
+        
+        else callbackResult('Abort Mission', undefined)
+    }, 2000)
+
+    console.log('Checking weather....')
+}
+const callbackResult = (error, result) => {
+  if (error) {
+    return console.log(error);
+  }
+  console.log(result);
+}
+
+doRocketLaunch('Good', callbackResult)
+//doRocketLaunch('Bad', callbackResult)

5-es6-objects.js

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+let name = "Imam"
+let myAge= 25
+
+let user = {
+    name, 
+    age: myAge,
+    location: 'Bangladesh'
+}
+// console.log(user) //{ name: 'Imam', age: 25, location: 'Bangladesh' }
+
+
+
+//Destructuring
+
+let product = {
+    label: "You don't know JS",
+    price: 10 + '$' ,
+    stock: 201,
+    salePrice: undefined,
+   // rating: 4.2
+}
+// let label = product.label
+// let price = product.price
+
+let {label: productLabel, price, rating = 5} = product
+//console.log(productLabel, price, rating )
+
+let transaction = (type, {label, price, stock = 0} = {}) => {
+    console.log(type, label, price, stock)
+}
+transaction('order', product)
+
+
+/****Objeect property */
+
+const userName = [
+    {
+        name: 'Imam'
+    },
+    {
+        name: 'Shuvro'
+    },
+    {
+        name: 'Santho'
+    }
+]
+console.log({ name })

6-raw-http.js

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+const https = require('https')
+
+let  lat = 23.7104, lon = 90.4074;  //Dhaka, BD
+
+const url = `https://api.openweathermap.org/data/2.5/onecall?lat=${lat}&lon=${lon}&units=metric&exclude=daily&appid=a914e84824e3adbafcdfc73e8b8889e4`
+
+const request =  https.request(url, (response) => {
+    let data = ''
+
+    response.on('data', (chunk) => {
+        console.log(chunk)
+        console.log('*********************************')
+        data = data + chunk.toString()
+    })
+    response.on('end', () => {
+        const body =  JSON.parse(data)
+        console.log(body)
+    })
+})
+request.on('error', (error) => {
+    //console.log('An error!', error)
+})
+
+request.end()

7-default-params.js

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+let greater = (name = '', age = 0) => {
+    console.log('Hello ' + name, '\t You are ' + age + ' years old')
+}
+
+greater('Imam')
+
+greater()
+greater( '', 24)
+
+greater('Imam ', 24 , 'extra')

8-promise-chaining.js

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+const add =  (a, b) => {
+  return new Promise((resolve, reject) => {
+    setTimeout(() => {
+      resolve(a + b)
+    }, 1000)
+  })
+}
+
+const sum = add(1, 2)
+  .then((sum) => {
+    console.log(sum)
+    return add(sum, 5)
+  })
+  .then((sum) => console.log(sum))
+  .catch((err) => console.log(err))

8-promises.js

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+const doRocketLaunch = (weather) => {
+  return new Promise((resolve, reject) => {
+    setTimeout(function gettingWeatherData() {
+      if (weather == "Good") resolve("Mission Success")
+      else reject("Abort Mission")
+    }, 2000)
+  })
+}
+
+doRocketLaunch("Good")
+  .then((result) => console.log(result))
+  .catch((error) => console.log(error))

9.async-await.js

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+const add = (a, b) => {
+  return new Promise((resolve, reject) => {
+    setTimeout(() => {
+      if (a < 0 || b < 0) reject(new Error('Negative number not supported'))
+      resolve(a + b)
+    }, 1000)
+  })
+}
+
+const doWork = async () => {
+  const sum = await add(1, 2)
+  const sum2 = await add(sum, 5)
+  const sum3 = await add(sum2, 10)
+
+  return sum3
+}
+doWork()
+  .then((sum) => console.log(sum))
+  .catch((e) => console.log(e))
+
+async function some(a) {
+  if (a < 10) throw new Error('Less then 10')
+  
+  return a + 10
+}
+
+async function another() {
+  try {
+    const a = await some(10)
+
+    console.log(a)
+  }
+  catch {
+    console.log(error)
+  }
+}
+
+ another()