benchmark: replace [].join() with ''.repeat()

Also add a benchmark to compare both ways to create strings.

PR-URL: https://github.com/nodejs/node/pull/12170
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

1 files changed, 35 insertions, 0 deletions

diff --git a/benchmark/es/string-repeat.js b/benchmark/es/string-repeat.js
new file mode 100644
index 0000000000..a6b389033a
--- /dev/null
+++ b/benchmark/es/string-repeat.js
@@ -0,0 +1,35 @@
+'use strict';
+
+const assert = require('assert');
+const common = require('../common.js');
+
+const configs = {
+  n: [1e3],
+  mode: ['Array', 'repeat'],
+  encoding: ['ascii', 'utf8'],
+  size: [1e1, 1e3, 1e6],
+};
+
+const bench = common.createBenchmark(main, configs);
+
+function main(conf) {
+  const n = +conf.n;
+  const size = +conf.size;
+  const character = conf.encoding === 'ascii' ? 'a' : '\ud83d\udc0e'; // '🐎'
+
+  let str;
+
+  if (conf.mode === 'Array') {
+    bench.start();
+    for (let i = 0; i < n; i++)
+      str = new Array(size + 1).join(character);
+    bench.end(n);
+  } else {
+    bench.start();
+    for (let i = 0; i < n; i++)
+      str = character.repeat(size);
+    bench.end(n);
+  }
+
+  assert.strictEqual([...str].length, size);
+}