有部分浏览器中没有Object.assign方法，则使用以下方式进行添加
if(typeof Object.assign != 'function') {
(function() {
Object.assign = function(target) {
'use strict';
if(target === undefined || target === null) {
throw new TypeError('Cannot convert undefined or null to object');
}
var output = Object(target);
for(var index = 1; index < arguments.length; index++) {
var source = arguments[index];
if(source !== undefined && source !== null) {
for(var nextKey in source) {
if(source.hasOwnProperty(nextKey)) {
output[nextKey] = source[nextKey];
}
}
}
}
return output;
};
})();
}
