diff --git a/lib/repl.js b/lib/repl.js
index 4c44e2aa4d47a7..a6123d93896d06 100644
--- a/lib/repl.js
+++ b/lib/repl.js
@@ -22,7 +22,7 @@
 /* A repl library that you can include in your own code to get a runtime
  * interface to your program.
  *
- *   var repl = require("repl");
+ *   const repl = require("repl");
  *   // start repl on stdin
  *   repl.start("prompt> ");
  *
@@ -372,7 +372,7 @@ function REPLServer(prompt,
 
       // After executing the current expression, store the values of RegExp
       // predefined properties back in `savedRegExMatches`
-      for (var idx = 1; idx < savedRegExMatches.length; idx += 1) {
+      for (let idx = 1; idx < savedRegExMatches.length; idx += 1) {
         savedRegExMatches[idx] = RegExp[`$${idx}`];
       }
 
@@ -636,8 +636,8 @@ function REPLServer(prompt,
     self.emit('exit');
   });
 
-  var sawSIGINT = false;
-  var sawCtrlD = false;
+  let sawSIGINT = false;
+  let sawCtrlD = false;
   const prioritizedSigintQueue = new Set();
   self.on('SIGINT', function onSigInt() {
     if (prioritizedSigintQueue.size > 0) {
@@ -877,7 +877,7 @@ REPLServer.prototype.close = function close() {
 };
 
 REPLServer.prototype.createContext = function() {
-  var context;
+  let context;
   if (this.useGlobal) {
     context = global;
   } else {
@@ -963,7 +963,7 @@ REPLServer.prototype.resetContext = function() {
 };
 
 REPLServer.prototype.displayPrompt = function(preserveCursor) {
-  var prompt = this._initialPrompt;
+  let prompt = this._initialPrompt;
   if (this[kBufferedCommandSymbol].length) {
     prompt = '...';
     const len = this.lines.level.length ? this.lines.level.length - 1 : 0;
@@ -993,7 +993,7 @@ function ArrayStream() {
   Stream.call(this);
 
   this.run = function(data) {
-    for (var n = 0; n < data.length; n++)
+    for (let n = 0; n < data.length; n++)
       this.emit('data', `${data[n]}\n`);
   };
 }
@@ -1018,7 +1018,7 @@ function isIdentifier(str) {
     return false;
   }
   const firstLen = first > 0xffff ? 2 : 1;
-  for (var i = firstLen; i < str.length; i += 1) {
+  for (let i = firstLen; i < str.length; i += 1) {
     const cp = str.codePointAt(i);
     if (!isIdentifierChar(cp)) {
       return false;
@@ -1056,7 +1056,7 @@ REPLServer.prototype.complete = function() {
 // given to the readline interface for handling tab completion.
 //
 // Example:
-//  complete('var foo = util.')
+//  complete('let foo = util.')
 //    -> [['util.print', 'util.debug', 'util.log', 'util.inspect'],
 //        'util.' ]
 //
@@ -1067,16 +1067,16 @@ function complete(line, callback) {
   if (this[kBufferedCommandSymbol] !== undefined &&
       this[kBufferedCommandSymbol].length) {
     // Get a new array of inputted lines
-    var tmp = this.lines.slice();
+    const tmp = this.lines.slice();
     // Kill off all function declarations to push all local variables into
     // global scope
-    for (var n = 0; n < this.lines.level.length; n++) {
-      var kill = this.lines.level[n];
+    for (let n = 0; n < this.lines.level.length; n++) {
+      const kill = this.lines.level[n];
       if (kill.isFunction)
         tmp[kill.line] = '';
     }
-    var flat = new ArrayStream();         // Make a new "input" stream.
-    var magic = new REPLServer('', flat); // Make a nested REPL.
+    const flat = new ArrayStream();         // Make a new "input" stream.
+    const magic = new REPLServer('', flat); // Make a nested REPL.
     replMap.set(magic, replMap.get(this));
     flat.run(tmp);                        // `eval` the flattened code.
     // All this is only profitable if the nested REPL does not have a
@@ -1087,13 +1087,12 @@ function complete(line, callback) {
     }
   }
 
-  var completions;
   // List of completion lists, one for each inheritance "level"
-  var completionGroups = [];
-  var completeOn, group, c;
+  let completionGroups = [];
+  let completeOn, group;
 
   // REPL commands (e.g. ".break").
-  var filter;
+  let filter;
   let match = line.match(/^\s*\.(\w*)$/);
   if (match) {
     completionGroups.push(Object.keys(this.commands));
@@ -1106,14 +1105,14 @@ function complete(line, callback) {
   } else if (match = line.match(requireRE)) {
     // require('...<Tab>')
     const exts = Object.keys(this.context.require.extensions);
-    var indexRe = new RegExp('^index(?:' + exts.map(regexpEscape).join('|') +
+    const indexRe = new RegExp('^index(?:' + exts.map(regexpEscape).join('|') +
                              ')$');
-    var versionedFileNamesRe = /-\d+\.\d+/;
+    const versionedFileNamesRe = /-\d+\.\d+/;
 
     completeOn = match[1];
-    var subdir = match[2] || '';
+    const subdir = match[2] || '';
     filter = match[1];
-    var dir, files, name, base, ext, abs, subfiles, isDirectory;
+    let dir, files, name, base, ext, abs, subfiles, isDirectory;
     group = [];
     let paths = [];
 
@@ -1211,7 +1210,7 @@ function complete(line, callback) {
   } else if (line.length === 0 || /\w|\.|\$/.test(line[line.length - 1])) {
     match = simpleExpressionRE.exec(line);
     if (line.length === 0 || match) {
-      var expr;
+      let expr;
       completeOn = (match ? match[0] : '');
       if (line.length === 0) {
         filter = '';
@@ -1220,19 +1219,19 @@ function complete(line, callback) {
         filter = '';
         expr = match[0].slice(0, match[0].length - 1);
       } else {
-        var bits = match[0].split('.');
+        const bits = match[0].split('.');
         filter = bits.pop();
         expr = bits.join('.');
       }
 
       // Resolve expr and get its completions.
-      var memberGroups = [];
+      const memberGroups = [];
       if (!expr) {
         // If context is instance of vm.ScriptContext
         // Get global vars synchronously
         if (this.useGlobal || vm.isContext(this.context)) {
           completionGroups.push(getGlobalLexicalScopeNames(this[kContextId]));
-          var contextProto = this.context;
+          let contextProto = this.context;
           while (contextProto = Object.getPrototypeOf(contextProto)) {
             completionGroups.push(
               filteredOwnPropertyNames.call(this, contextProto));
@@ -1247,7 +1246,7 @@ function complete(line, callback) {
               if (filter !== '') addCommonWords(completionGroups);
             } else if (Array.isArray(globals[0])) {
               // Add grouped globals
-              for (var n = 0; n < globals.length; n++)
+              for (let n = 0; n < globals.length; n++)
                 completionGroups.push(globals[n]);
             } else {
               completionGroups.push(globals);
@@ -1272,8 +1271,8 @@ function complete(line, callback) {
             }
             // Works for non-objects
             try {
-              var sentinel = 5;
-              var p;
+              let sentinel = 5;
+              let p;
               if (typeof obj === 'object' || typeof obj === 'function') {
                 p = Object.getPrototypeOf(obj);
               } else {
@@ -1316,7 +1315,7 @@ function complete(line, callback) {
   function completionGroupsLoaded() {
     // Filter, sort (within each group), uniq and merge the completion groups.
     if (completionGroups.length && filter) {
-      var newCompletionGroups = [];
+      const newCompletionGroups = [];
       for (let i = 0; i < completionGroups.length; i++) {
         group = completionGroups[i]
           .filter((elem) => elem.indexOf(filter) === 0);
@@ -1327,8 +1326,10 @@ function complete(line, callback) {
       completionGroups = newCompletionGroups;
     }
 
+    let completions;
+
     if (completionGroups.length) {
-      var uniq = {};  // Unique completions across all groups
+      const uniq = {};  // Unique completions across all groups
       completions = [];
       // Completion group 0 is the "closest"
       // (least far up the inheritance chain)
@@ -1336,8 +1337,8 @@ function complete(line, callback) {
       for (let i = 0; i < completionGroups.length; i++) {
         group = completionGroups[i];
         group.sort();
-        for (var j = group.length - 1; j >= 0; j--) {
-          c = group[j];
+        for (let j = group.length - 1; j >= 0; j--) {
+          const c = group[j];
           if (!ObjectPrototype.hasOwnProperty(uniq, c)) {
             completions.unshift(c);
             uniq[c] = true;
@@ -1361,9 +1362,9 @@ function longestCommonPrefix(arr = []) {
 
   const first = arr[0];
   // complexity: O(m * n)
-  for (var m = 0; m < first.length; m++) {
+  for (let m = 0; m < first.length; m++) {
     const c = first[m];
-    for (var n = 1; n < cnt; n++) {
+    for (let n = 1; n < cnt; n++) {
       const entry = arr[n];
       if (m >= entry.length || c !== entry[m]) {
         return first.substring(0, m);
@@ -1506,7 +1507,7 @@ function defineDefaultCommands(repl) {
     }
   });
 
-  var clearMessage;
+  let clearMessage;
   if (repl.useGlobal) {
     clearMessage = 'Alias for .break';
   } else {
@@ -1539,11 +1540,11 @@ function defineDefaultCommands(repl) {
         (max, name) => Math.max(max, name.length),
         0
       );
-      for (var n = 0; n < names.length; n++) {
-        var name = names[n];
-        var cmd = this.commands[name];
-        var spaces = ' '.repeat(longestNameLength - name.length + 3);
-        var line = `.${name}${cmd.help ? spaces + cmd.help : ''}\n`;
+      for (let n = 0; n < names.length; n++) {
+        const name = names[n];
+        const cmd = this.commands[name];
+        const spaces = ' '.repeat(longestNameLength - name.length + 3);
+        const line = `.${name}${cmd.help ? spaces + cmd.help : ''}\n`;
         this.outputStream.write(line);
       }
       this.outputStream.write('\nPress ^C to abort current expression, ' +