复制 日期、数组、对象

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    function clone(obj) {
        // Handle the 3 simple types, and null or undefined
        if (null == obj || "object" != typeof obj) return obj;

        // Handle Date
        if (obj instanceof Date) {
            var copy = new Date();
            copy.setTime(obj.getTime());
            return copy;
        }

        // Handle Array
        if (obj instanceof Array) {
            var copy = [];
            var len = obj.length;
            for (var i = 0; i < len; ++i) {
                copy[i] = clone(obj[i]);
            }
            return copy;
        }

        // Handle Object
        if (obj instanceof Object) {
            var copy = {};
            for (var attr in obj) {
                if (obj.hasOwnProperty(attr)) copy[attr] = clone(obj[attr]);
            }
            return copy;
        }

        throw new Error("Unable to copy obj! Its type isn't supported.");
    }