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实现Object keys
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if (!Object.keys) {
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Object.keys = (function () {
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var hasOwnProperty = Object.prototype.hasOwnProperty,
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hasDontEnumBug = !({toString: null}).propertyIsEnumerable('toString'),
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dontEnums = [
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'toString',
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'toLocaleString',
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'valueOf',
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'hasOwnProperty',
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'isPrototypeOf',
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'propertyIsEnumerable',
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'constructor'
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],
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dontEnumsLength = dontEnums.length;
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return function (obj) {
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if (typeof obj !== 'object' && typeof obj !== 'function' || obj === null) throw new TypeError('Object.keys called on non-object');
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var result = [];
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for (var prop in obj) {
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if (hasOwnProperty.call(obj, prop)) result.push(prop);
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}
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if (hasDontEnumBug) {
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for (var i=0; i < dontEnumsLength; i++) {
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if (hasOwnProperty.call(obj, dontEnums[i])) result.push(dontEnums[i]);
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}
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}
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return result;
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};
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})();
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}
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