for-of optimization

Author: aminya

README.md

@@ -8,6 +8,8 @@ Benchmarks are done inside Atom (using script package) and Webstorm.
 - ES6 and above: traditional `for` is **faster** than `for-of` that is faster than `for-in`
 - ES5 and lower:Traditional `for` is **similar to** `for-of` and both faster than `for-in`.
 
+If you notice, you see by targeting ES5 the TypeScript compiler converts `for-of` to the `traditional-for`, and that makes it faster than the original `for-of`!!
+
 ```typescript
 // Traditional
   let sum = 0
@@ -133,3 +135,46 @@ for (let i = 0; i < arr_return().length; ++i) {
     Fastest is for-traditional-const,for-traditional-length-lookup
 
 </details>
+
+
+### `for-of` optimization
+
+- in all versions: full array look-up in the `for-head` is much slower.
+
+If you notice, you see by targeting ES5 the TypeScript compiler converts `for-of` to the `traditional-for`, and that makes it faster than the original `for-of`!!
+
+```typescript
+// for-of
+  let sum = 0
+  for (const a of arr) {
+    sum += a
+  }
+// for-of-full-array-lookup
+  let sum = 0
+  for (const a of arr_return()) {
+    sum += a
+  }
+```
+
+<details>
+<summary>Benchmark-Result</summary>
+
+    ES2020:
+
+    for-of x 83,144 ops/sec ±0.52% (93 runs sampled)
+    for-of-full-lookup x 13,930 ops/sec ±0.62% (95 runs sampled)
+    Fastest is for-of
+
+    ES 6:
+
+    for-of x 83,036 ops/sec ±0.43% (95 runs sampled)
+    for-of-full-lookup x 13,779 ops/sec ±0.90% (96 runs sampled)
+    Fastest is for-of
+
+    ES5:
+
+    for-of x 110,799 ops/sec ±0.15% (96 runs sampled)
+    for-of-full-lookup x 15,122 ops/sec ±0.74% (95 runs sampled)
+    Fastest is for-of
+
+</details>

src/for-of-array.ts

@@ -0,0 +1,36 @@
+const Benchmark = require("benchmark")
+let suite = new Benchmark.Suite()
+
+const arr: number[] = []
+for (let i = 0; i < 10000; ++i) arr.push(i)
+
+// add tests
+suite.add("for-of", function() {
+  let sum = 0
+  for (const a of arr) {
+    sum += a
+  }
+})
+
+function arr_return() {
+  const arr2: number[] = []
+  for (let i = 0; i < 10000; ++i) arr2.push(i)
+  return arr2
+}
+
+suite.add("for-of-full-lookup", function() {
+  let sum = 0
+  for (const a of arr_return()) {
+    sum += a
+  }
+})
+
+// add listeners
+suite.on("cycle", function(event) {
+  console.log(String(event.target))
+})
+suite.on("complete", function() {
+  console.log("Fastest is " + this.filter("fastest").map("name"))
+})
+// run async
+suite.run({ async: true })