benchmark: add benchmark for string concatenations

PR-URL: https://github.com/nodejs/node/pull/12455
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

benchmark/es/string-concatenations.js

@@ -0,0 +1,69 @@
+'use strict';
+
+const common = require('../common.js');
+
+const configs = {
+  n: [1e3],
+  mode: [
+    'multi-concat',
+    'multi-join',
+    'multi-template',
+    'to-string-string',
+    'to-string-concat',
+    'to-string-template',
+  ],
+};
+
+const bench = common.createBenchmark(main, configs);
+
+
+function main(conf) {
+  const n = +conf.n;
+  const mode = conf.mode;
+
+  const str = 'abc';
+  const num = 123;
+
+  let string;
+
+  switch (mode) {
+    case 'multi-concat':
+      bench.start();
+      for (let i = 0; i < n; i++)
+        string = '...' + str + ', ' + num + ', ' + str + ', ' + num + '.';
+      bench.end(n);
+      break;
+    case 'multi-join':
+      bench.start();
+      for (let i = 0; i < n; i++)
+        string = ['...', str, ', ', num, ', ', str, ', ', num, '.'].join('');
+      bench.end(n);
+      break;
+    case 'multi-template':
+      bench.start();
+      for (let i = 0; i < n; i++)
+        string = `...${str}, ${num}, ${str}, ${num}.`;
+      bench.end(n);
+      break;
+    case 'to-string-string':
+      bench.start();
+      for (let i = 0; i < n; i++)
+        string = String(num);
+      bench.end(n);
+      break;
+    case 'to-string-concat':
+      bench.start();
+      for (let i = 0; i < n; i++)
+        string = '' + num;
+      bench.end(n);
+      break;
+    case 'to-string-template':
+      bench.start();
+      for (let i = 0; i < n; i++)
+        string = `${num}`;
+      bench.end(n);
+      break;
+  }
+
+  return string;
+}