diff --git a/benchmark/http_simple.js b/benchmark/http_simple.js
index 0f36d3b6ce3ebd..9a580de2c0f665 100644
--- a/benchmark/http_simple.js
+++ b/benchmark/http_simple.js
@@ -4,7 +4,7 @@ var http = require('http');
 
 var port = parseInt(process.env.PORT || 8000);
 
-var fixed = makeString(20 * 1024, 'C'),
+var fixed = 'C'.repeat(20 * 1024),
   storedBytes = {},
   storedBuffer = {},
   storedUnicode = {};
@@ -42,7 +42,7 @@ var server = module.exports = http.createServer(function(req, res) {
     if (n <= 0)
       throw new Error('bytes called with n <= 0');
     if (storedBytes[n] === undefined) {
-      storedBytes[n] = makeString(n, 'C');
+      storedBytes[n] = 'C'.repeat(n);
     }
     body = storedBytes[n];
 
@@ -63,7 +63,7 @@ var server = module.exports = http.createServer(function(req, res) {
     if (n <= 0)
       throw new Error('unicode called with n <= 0');
     if (storedUnicode[n] === undefined) {
-      storedUnicode[n] = makeString(n, '\u263A');
+      storedUnicode[n] = '\u263A'.repeat(n);
     }
     body = storedUnicode[n];
 
@@ -107,14 +107,6 @@ var server = module.exports = http.createServer(function(req, res) {
   }
 });
 
-function makeString(size, c) {
-  var s = '';
-  while (s.length < size) {
-    s += c;
-  }
-  return s;
-}
-
 server.listen(port, function() {
   if (module === require.main)
     console.error('Listening at http://127.0.0.1:' + port + '/');
diff --git a/benchmark/http_simple_auto.js b/benchmark/http_simple_auto.js
index 6f56879cc08aaa..bbdc2ed6d74071 100644
--- a/benchmark/http_simple_auto.js
+++ b/benchmark/http_simple_auto.js
@@ -13,11 +13,7 @@ var spawn = require('child_process').spawn;
 
 var port = parseInt(process.env.PORT || 8000);
 
-var fixed = '';
-var i;
-for (i = 0; i < 20 * 1024; i++) {
-  fixed += 'C';
-}
+var fixed = 'C'.repeat(20 * 1024);
 
 var stored = {};
 var storedBuffer = {};
@@ -30,16 +26,14 @@ var server = http.createServer(function(req, res) {
   var n_chunks = parseInt(commands[3], 10);
   var status = 200;
   var n;
+  var i;
 
   if (command == 'bytes') {
     n = parseInt(arg, 10);
     if (n <= 0)
       throw new Error('bytes called with n <= 0');
     if (stored[n] === undefined) {
-      stored[n] = '';
-      for (i = 0; i < n; i++) {
-        stored[n] += 'C';
-      }
+      stored[n] = 'C'.repeat(n);
     }
     body = stored[n];
   } else if (command == 'buffer') {
diff --git a/benchmark/static_http_server.js b/benchmark/static_http_server.js
index 804f83c208bb39..43c493675933e7 100644
--- a/benchmark/static_http_server.js
+++ b/benchmark/static_http_server.js
@@ -9,10 +9,7 @@ var bytes = 1024 * 5;
 var requests = 0;
 var responses = 0;
 
-var body = '';
-for (var i = 0; i < bytes; i++) {
-  body += 'C';
-}
+var body = 'C'.repeat(bytes);
 
 var server = http.createServer(function(req, res) {
   res.writeHead(200, {
diff --git a/lib/_debugger.js b/lib/_debugger.js
index 5ce1b16960b0ef..3681ce58802a62 100644
--- a/lib/_debugger.js
+++ b/lib/_debugger.js
@@ -1008,11 +1008,7 @@ function leftPad(n, prefix, maxN) {
   const nchars = Math.max(2, String(maxN).length) + 1;
   const nspaces = nchars - s.length - 1;
 
-  for (var i = 0; i < nspaces; i++) {
-    prefix += ' ';
-  }
-
-  return prefix + s;
+  return prefix + ' '.repeat(nspaces) + s;
 }
 
 
diff --git a/test/fixtures/print-chars.js b/test/fixtures/print-chars.js
index e2223e20f25508..b9707fbf75fa67 100644
--- a/test/fixtures/print-chars.js
+++ b/test/fixtures/print-chars.js
@@ -2,9 +2,4 @@ var assert = require('assert');
 
 var n = parseInt(process.argv[2]);
 
-var s = '';
-for (var i = 0; i < n; i++) {
-  s += 'c';
-}
-
-process.stdout.write(s);
+process.stdout.write('c'.repeat(n));
diff --git a/test/parallel/test-buffer.js b/test/parallel/test-buffer.js
index 61f3aa08b70736..99d1c129ca8805 100644
--- a/test/parallel/test-buffer.js
+++ b/test/parallel/test-buffer.js
@@ -612,10 +612,7 @@ assert.equal(Buffer('=bad'.repeat(1e4), 'base64').length, 0);
 {
   // Creating buffers larger than pool size.
   const l = Buffer.poolSize + 5;
-  let s = '';
-  for (let i = 0; i < l; i++) {
-    s += 'h';
-  }
+  const s = 'h'.repeat(l);
 
   const b = new Buffer(s);
 
diff --git a/test/parallel/test-fs-realpath.js b/test/parallel/test-fs-realpath.js
index dcc28ce4d99afa..aa397e51d16409 100644
--- a/test/parallel/test-fs-realpath.js
+++ b/test/parallel/test-fs-realpath.js
@@ -219,7 +219,7 @@ function test_cyclic_link_overprotection(callback) {
   var folder = cycles + '/folder';
   var link = folder + '/cycles';
   var testPath = cycles;
-  for (var i = 0; i < 10; i++) testPath += '/folder/cycles';
+  testPath += '/folder/cycles'.repeat(10);
   try {fs.unlinkSync(link);} catch (ex) {}
   fs.symlinkSync(cycles, link, 'dir');
   unlink.push(link);
diff --git a/test/parallel/test-http-full-response.js b/test/parallel/test-http-full-response.js
index 8472a84fb9fac9..767efa3cd6657e 100644
--- a/test/parallel/test-http-full-response.js
+++ b/test/parallel/test-http-full-response.js
@@ -7,10 +7,7 @@ var exec = require('child_process').exec;
 
 var bodyLength = 12345;
 
-var body = '';
-for (var i = 0; i < bodyLength; i++) {
-  body += 'c';
-}
+var body = 'c'.repeat(bodyLength);
 
 var server = http.createServer(function(req, res) {
   res.writeHead(200, {
diff --git a/test/parallel/test-http-pipeline-regr-2639.js b/test/parallel/test-http-pipeline-regr-2639.js
index f1f75bff650ac5..c7cebb9d46a19f 100644
--- a/test/parallel/test-http-pipeline-regr-2639.js
+++ b/test/parallel/test-http-pipeline-regr-2639.js
@@ -22,9 +22,8 @@ var server = http.createServer(function(req, res) {
 }).listen(common.PORT, function() {
   const s = net.connect(common.PORT);
 
-  var big = '';
-  for (var i = 0; i < COUNT; i++)
-    big += 'GET / HTTP/1.0\r\n\r\n';
+  var big = 'GET / HTTP/1.0\r\n\r\n'.repeat(COUNT);
+
   s.write(big);
   s.resume();
 });
diff --git a/test/parallel/test-net-large-string.js b/test/parallel/test-net-large-string.js
index 387f3f4f8c1dd3..26227c8e759787 100644
--- a/test/parallel/test-net-large-string.js
+++ b/test/parallel/test-net-large-string.js
@@ -4,10 +4,7 @@ var assert = require('assert');
 var net = require('net');
 
 var kPoolSize = 40 * 1024;
-var data = '';
-for (var i = 0; i < kPoolSize; ++i) {
-  data += 'あ'; // 3bytes
-}
+var data = 'あ'.repeat(kPoolSize);
 var receivedSize = 0;
 var encoding = 'UTF-8';
 
diff --git a/test/pummel/test-https-large-response.js b/test/pummel/test-https-large-response.js
index 4a15b29cd19467..1979c6737f76b3 100644
--- a/test/pummel/test-https-large-response.js
+++ b/test/pummel/test-https-large-response.js
@@ -16,12 +16,9 @@ var options = {
 };
 
 var reqCount = 0;
-var body = '';
 
 process.stdout.write('build body...');
-for (var i = 0; i < 1024 * 1024; i++) {
-  body += 'hello world\n';
-}
+var body = 'hello world\n'.repeat(1024 * 1024);
 process.stdout.write('done\n');
 
 var server = https.createServer(options, function(req, res) {
diff --git a/test/pummel/test-net-many-clients.js b/test/pummel/test-net-many-clients.js
index 6d9dde1ddbc863..cb766ec1a47c63 100644
--- a/test/pummel/test-net-many-clients.js
+++ b/test/pummel/test-net-many-clients.js
@@ -11,10 +11,7 @@ var connections_per_client = 5;
 // measured
 var total_connections = 0;
 
-var body = '';
-for (var i = 0; i < bytes; i++) {
-  body += 'C';
-}
+var body = 'C'.repeat(bytes);
 
 var server = net.createServer(function(c) {
   console.log('connected');
diff --git a/test/pummel/test-net-throttle.js b/test/pummel/test-net-throttle.js
index 54956b789aed93..e98a6c765a905e 100644
--- a/test/pummel/test-net-throttle.js
+++ b/test/pummel/test-net-throttle.js
@@ -9,10 +9,7 @@ var chars_recved = 0;
 var npauses = 0;
 
 console.log('build big string');
-var body = '';
-for (var i = 0; i < N; i++) {
-  body += 'C';
-}
+body = 'C'.repeat(N);
 
 console.log('start server on port ' + common.PORT);
 
diff --git a/test/pummel/test-tls-throttle.js b/test/pummel/test-tls-throttle.js
index 67efb61b7e66aa..0e5cd455c8c4c4 100644
--- a/test/pummel/test-tls-throttle.js
+++ b/test/pummel/test-tls-throttle.js
@@ -12,16 +12,10 @@ if (!common.hasCrypto) {
 var tls = require('tls');
 var fs = require('fs');
 
-
-var body = '';
-
 process.stdout.write('build body...');
-for (var i = 0; i < 1024 * 1024; i++) {
-  body += 'hello world\n';
-}
+var body = 'hello world\n'.repeat(1024 * 1024);
 process.stdout.write('done\n');
 
-
 var options = {
   key: fs.readFileSync(common.fixturesDir + '/keys/agent2-key.pem'),
   cert: fs.readFileSync(common.fixturesDir + '/keys/agent2-cert.pem')