CoffeeScript array comprehensions — модно, стильно, медленно

'use strict';

const MAX = 1000;
const source = new Array(MAX);

for (let i = 0; i < MAX; i++) {
	source[i] = i * 2;
}

// Максимально приближеный к нативному
function trueMyMap(array, callback, thisArg) {
	const result = [];
	const length = array.length;

	for (let i = 0; i < length; i++) {
		if (i in array) {
			result.push(callback.call(thisArg, array[i], i, array));
		}
	}

	return result;
}

// Простой и быстрый (без учета «дырок»)
function simpleMap(array, callback, thisArg) {
	const result = [];
	const length = array.length;

	for (let i = 0; i < length; i++) {
		result.push(callback.call(thisArg, array[i], i, array));
	}

	return result;
}

// Оптимизированный (без учета «дырок»)
function optimizedMap(array, callback, thisArg) {
	const length = array.length;
	const result = new Array(length);
	const argsLength = callback.length;

	for (let i = 0; i < length; i++) {
		if (thisArg !== void 0) {
			result.push(callback.call(thisArg, array[i], i, array));
		} else if (argsLength <= 1) {
			result.push(callback(array[i]));
		} else if (argsLength === 2) {
			result.push(callback(array[i], i));
		} else {
			result.push(callback(array[i], i, array));
		}
	}

	return result;
}

// Хелпер для запуска тестов
function perf(name, tests) {
	console.log(name);

	Object.keys(tests).forEach(function (name) {
		const callback = tests[name];
		console.time('  ' + name);

		for (let i = 0; i < 1e4; i++) {
			callback();
		}

		console.timeEnd('  ' + name);
	});
}

//
// Тесты
//
perf('Array#map(val)', {
	'native': function () {
		source.map(function (val) {
			return val;
		});
	},

	'trueMyMap': function () {
		trueMyMap(source, function (val) {
			return val;
		});
	},

	'simple': function () {
		simpleMap(source, function (val) {
			return val;
		});
	},

	'optimized': function () {
		optimizedMap(source, function (val) {
			return val;
		});
	}
});

perf('Array#map(val, idx)', {
	'native': function () {
		source.map(function (val, idx) {
			return val * idx;
		});
	},
	
	'simple': function () {
		simpleMap(source, function (val, idx) {
			return val * idx;
		});
	},

	'optimized': function () {
		optimizedMap(source, function (val, idx) {
			return val * idx;
		});
	}
});

perf('Array#map(val, idx, array)', {
	'native': function () {
		source.map(function (val, idx, array) {
			return val * idx + array.length;
		});
	},

	'simple': function () {
		simpleMap(source, function (val, idx, array) {
			return val * idx + array.length;
		});
	},

	'optimized': function () {
		optimizedMap(source, function (val, idx, array) {
			return val * idx + array.length;
		});
	}
});

perf('Array#map(val, idx, array) + thisArg', {
	'native': function () {
		source.map(function (val, idx, array) {
			return val * idx + array.length * this.foo;
		}, {foo: 123});
	},

	'simple': function () {
		simpleMap(source, function (val, idx, array) {
			return val * idx + array.length * this.foo;
		}, {foo: 123});
	},

	'optimized': function () {
		optimizedMap(source, function (val, idx, array) {
			return val * idx + array.length * this.foo;
		}, {foo: 123});
	}
});

Array#map(val)
  native: 791ms
  trueMyMap: 836ms
  simple: 210ms
  optimized: 164ms
Array#map(val, idx)
  native: 823ms
  simple: 222ms
  optimized: 186ms
Array#map(val, idx, array)
  native: 770ms
  simple: 190ms
  optimized: 203ms
Array#map(val, idx, array) + thisArg
  native: 768ms
  simple: 180ms
  optimized: 199ms