if (this == null) { thrownewTypeError('this is null or not defined'); }
// 1. Let O be the result of calling toObject() passing the // |this| value as the argument. var O = Object(this);
// 2. Let lenValue be the result of calling the Get() internal // method of O with the argument "length". // 3. Let len be toUint32(lenValue). var len = O.length >>> 0;
// 4. If isCallable(callback) is false, throw a TypeError exception. // See: http://es5.github.com/#x9.11 if (typeof callback !== 'function') { thrownewTypeError(callback + ' is not a function'); }
// 5. If thisArg was supplied, let T be thisArg; else let // T be undefined. if (arguments.length > 1) { T = arguments[1]; }
// 6. Let k be 0. k = 0;
// 7. Repeat while k < len. while (k < len) {
var kValue;
// a. Let Pk be ToString(k). // This is implicit for LHS operands of the in operator. // b. Let kPresent be the result of calling the HasProperty // internal method of O with argument Pk. // This step can be combined with c. // c. If kPresent is true, then if (k in O) {
// i. Let kValue be the result of calling the Get internal // method of O with argument Pk. kValue = O[k];
// ii. Call the Call internal method of callback with T as // the this value and argument list containing kValue, k, and O. callback.call(T, kValue, k, O); } // d. Increase k by 1. k++; } // 8. return undefined. }; }
摘抄最重要的部分:
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/* O 为传入数组 len 为传入数组长度 callback 为传入回调函数 */ while (k < len) { var kValue; if (k in O) { kValue = O[k]; callback.call(T, kValue, k, O); } k++; }