Differences in Function Scope: A Comparison of ECMAScript 6 and ECMAScript 5

What are the advantages of ES6 compared to ES5 when it comes to block scope functions? Although the blocks may look similar in both cases, what impact does it have performance-wise and which approach is more efficient?

ES6 Block

{
        function foo() {
            return 1;
        }

        foo() === 1;
        {
            function foo() {
                return 2;
            }

            foo() === 2;
        }
        foo() === 1;
    }
    

ES5 Block

(function () {
        var foo = function () {
            return 1;
        }
        foo() === 1;
        (function () {
            var foo = function () {
                return 2;
            }
            foo() === 2;
        })();
        foo() === 1;
    })();
    

Answer №1

Check out this speed test to see which method performs better:

document.getElementById('btn').addEventListener('click', ({ target }) => {
  target.disabled = true;
  target.innerHTML = "Running…";
  const suite = new Benchmark.Suite();
  document.getElementById('ES6').style.fontWeight = '';
  document.getElementById('ES5').style.fontWeight = '';
  suite.add('ES6', () => {
    {
        function foo() {
            return 1;
        }
        foo() === 1;
        {
            function foo() {
                return 2;
            }
            foo() === 2;
        }
        foo() === 1;
    }
  }).add('ES5', () => {
    (function () {
        var foo = function () {
            return 1;
        }
        foo() === 1;
        (function () {
            var foo = function () {
                return 2;
            }
            foo() === 2;
        })();
        foo() === 1;
    })();
  })
  .on('cycle', ({target: bench}) => document.getElementById(bench.name).textContent = `${bench.name}: ~${Benchmark.formatNumber(bench.hz|0)} ops/sec (~${Benchmark.formatNumber(Math.round(1e9/bench.hz))} ns/op)`)
  .on('complete', function() {
    const el = document.getElementById(this.filter('fastest').map('name')[0]),
          hz = this.filter('fastest').map('hz')[0],
          others = this.filter('slowest').map('hz'),
          avg = others.reduce((a, b) => a + b, 0) / others.length;
    el.style.fontWeight = 'bold';
    el.textContent += ` \u{1f451} ${Math.round((1 - avg / hz) * 100, 2)}% faster`;
    target.disabled = false;
    target.innerHTML = "Run";
  })
  .run({ 'async': true });
});
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.2/lodash.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/benchmark/2.1.2/benchmark.min.js"></script>
<ul>
  <li id="ES6"></li>
  <li id="ES5"></li>
</ul>
<button id="btn">Run</button>

Results on my device:

  • ES6: ~3,896,305 ops/sec (~257 ns/op) 👑 40% faster
  • ES5: ~2,425,847 ops/sec (~412 ns/op)

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