jfsiii/index.html

## index.html
<!doctype html>
<body>
  <script>
    // based on https://github.com/paulirish/memory-stats.js/blob/6fa0f359134c4668bd9b931b95156bae1073e8eb/memory-stats.js#L70-L79
    function bytesToSize( bytes, nFractDigit ){
      var sizes = ['Bytes', 'KB', 'MB', 'GB', 'TB']
      if (bytes === 0) return 'n/a'
      nFractDigit	= nFractDigit !== undefined ? nFractDigit : 0
      var precision = Math.pow(10, nFractDigit)
      var i = Math.floor(Math.log(bytes) / Math.log(1024))
      return Math.round(bytes*precision / Math.pow(1024, i))/precision + ' ' + sizes[i]
    }

    function profile(fn, label) {
      gc() // requires --js-flags="--expose-gc" flag
      const startMem = performance.memory.usedJSHeapSize
      performance.mark('start')
      fn()
      performance.mark('end')
      // need --enable-precise-memory-info flag for accurate before/after values
      const endMem = performance.memory.usedJSHeapSize
      const totalMem =  bytesToSize((endMem - startMem), 2)
      performance.measure(`${label} ${totalMem}`, 'start', 'end')
      gc() // requires --js-flags="--expose-gc" flag
    }

    function mapFn(v, i) { return i * 2 }
    var array = Array.from({length: 1e7}, mapFn)
    var string ="x".repeat(array.length)
    var pojo = {length: array.length}
  </script>

  <script>
    profile(() => array.map(mapFn), 'array.map(mapFn)')
    // 76.43 MB @ 1.79 sec (no GC?)

    profile(() => Array.from(array, mapFn), 'Array.from(array, mapFn)')
    // 84.62 MB @ 2.36 sec (24.3ms / 1% in GC)

    profile(() => Array.from(array).map(mapFn), 'Array.from(array).map(mapFn)')
    // 218.05 MB @ 3.62 sec (11.1ms / 0.3% in GC)

    profile(() => Array.from(string, mapFn), 'Array.from(string, mapFn)')
    // 150.67 MB @ 2.25 sec (12.8 ms / 0.6% in GC)

    profile(() => Array.from(string).map(mapFn), 'Array.from(string).map(mapFn)')
    // 227.17 MB @ 3.71 sec (7.9 ms / 0.3% in GC)

    profile(() => Array.from(pojo, mapFn), 'Array.from(pojo, mapFn)')
    // 76.32 MB @ 1.07 sec (no GC?)

    profile(() => Array.from(pojo).map(mapFn), 'Array.from(pojo).map(mapFn)')
    // 152.62 MB @ 2.63 sec (no GC?)
  </script>
</body>
	<!doctype html>
	<body>
	<script>
	// based on https://github.com/paulirish/memory-stats.js/blob/6fa0f359134c4668bd9b931b95156bae1073e8eb/memory-stats.js#L70-L79
	function bytesToSize( bytes, nFractDigit ){
	var sizes = ['Bytes', 'KB', 'MB', 'GB', 'TB']
	if (bytes === 0) return 'n/a'
	nFractDigit = nFractDigit !== undefined ? nFractDigit : 0
	var precision = Math.pow(10, nFractDigit)
	var i = Math.floor(Math.log(bytes) / Math.log(1024))
	return Math.round(bytes*precision / Math.pow(1024, i))/precision + ' ' + sizes[i]
	}

	function profile(fn, label) {
	gc() // requires --js-flags="--expose-gc" flag
	const startMem = performance.memory.usedJSHeapSize
	performance.mark('start')
	fn()
	performance.mark('end')
	// need --enable-precise-memory-info flag for accurate before/after values
	const endMem = performance.memory.usedJSHeapSize
	const totalMem = bytesToSize((endMem - startMem), 2)
	performance.measure(`${label} ${totalMem}`, 'start', 'end')
	gc() // requires --js-flags="--expose-gc" flag
	}

	function mapFn(v, i) { return i * 2 }
	var array = Array.from({length: 1e7}, mapFn)
	var string ="x".repeat(array.length)
	var pojo = {length: array.length}
	</script>

	<script>
	profile(() => array.map(mapFn), 'array.map(mapFn)')
	// 76.43 MB @ 1.79 sec (no GC?)

	profile(() => Array.from(array, mapFn), 'Array.from(array, mapFn)')
	// 84.62 MB @ 2.36 sec (24.3ms / 1% in GC)

	profile(() => Array.from(array).map(mapFn), 'Array.from(array).map(mapFn)')
	// 218.05 MB @ 3.62 sec (11.1ms / 0.3% in GC)

	profile(() => Array.from(string, mapFn), 'Array.from(string, mapFn)')
	// 150.67 MB @ 2.25 sec (12.8 ms / 0.6% in GC)

	profile(() => Array.from(string).map(mapFn), 'Array.from(string).map(mapFn)')
	// 227.17 MB @ 3.71 sec (7.9 ms / 0.3% in GC)

	profile(() => Array.from(pojo, mapFn), 'Array.from(pojo, mapFn)')
	// 76.32 MB @ 1.07 sec (no GC?)

	profile(() => Array.from(pojo).map(mapFn), 'Array.from(pojo).map(mapFn)')
	// 152.62 MB @ 2.63 sec (no GC?)
	</script>
	</body>