76 lines
2.4 KiB
JavaScript
76 lines
2.4 KiB
JavaScript
// Production steps of ECMA-262, Edition 6, 22.1.2.1
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// Reference: https://people.mozilla.org/~jorendorff/es6-draft.html#sec-array.from
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Array.from = (function () {
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var toStr = Object.prototype.toString;
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var isCallable = function (fn) {
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return typeof fn === 'function' || toStr.call(fn) === '[object Function]';
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};
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var toInteger = function (value) {
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var number = Number(value);
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if (isNaN(number)) { return 0; }
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if (number === 0 || !isFinite(number)) { return number; }
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return (number > 0 ? 1 : -1) * Math.floor(Math.abs(number));
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};
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var maxSafeInteger = Math.pow(2, 53) - 1;
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var toLength = function (value) {
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var len = toInteger(value);
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return Math.min(Math.max(len, 0), maxSafeInteger);
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};
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// The length property of the from method is 1.
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return function from(arrayLike/*, mapFn, thisArg */) {
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// 1. Let C be the this value.
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var C = this;
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// 2. Let items be ToObject(arrayLike).
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var items = Object(arrayLike);
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// 3. ReturnIfAbrupt(items).
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if (arrayLike == null) {
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throw new TypeError("Array.from requires an array-like object - not null or undefined");
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}
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// 4. If mapfn is undefined, then let mapping be false.
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var mapFn = arguments.length > 1 ? arguments[1] : void undefined;
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var T;
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if (typeof mapFn !== 'undefined') {
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// 5. else
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// 5. a If IsCallable(mapfn) is false, throw a TypeError exception.
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if (!isCallable(mapFn)) {
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throw new TypeError('Array.from: when provided, the second argument must be a function');
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}
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// 5. b. If thisArg was supplied, let T be thisArg; else let T be undefined.
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if (arguments.length > 2) {
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T = arguments[2];
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}
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}
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// 10. Let lenValue be Get(items, "length").
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// 11. Let len be ToLength(lenValue).
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var len = toLength(items.length);
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// 13. If IsConstructor(C) is true, then
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// 13. a. Let A be the result of calling the [[Construct]] internal method of C with an argument list containing the single item len.
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// 14. a. Else, Let A be ArrayCreate(len).
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var A = isCallable(C) ? Object(new C(len)) : new Array(len);
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// 16. Let k be 0.
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var k = 0;
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// 17. Repeat, while k < len… (also steps a - h)
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var kValue;
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while (k < len) {
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kValue = items[k];
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if (mapFn) {
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A[k] = typeof T === 'undefined' ? mapFn(kValue, k) : mapFn.call(T, kValue, k);
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} else {
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A[k] = kValue;
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}
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k += 1;
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}
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// 18. Let putStatus be Put(A, "length", len, true).
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A.length = len;
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// 20. Return A.
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return A;
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};
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}()); |