js如何将两个对象合并成一个对象？

1. object.assign(a, b)
2. let a = {
   ...a,

...b
}

es2015 Object.assign()

var o1 = { a: 1 };
var o2 = { b: 2 };
var o3 = { c: 3 };

var obj = Object.assign(o1, o2, o3);
console.log(obj); // { a: 1, b: 2, c: 3 }
console.log(o1);  // { a: 1, b: 2, c: 3 }, 注意目标对象自身也会改变。
Polyfill
if (!Object.assign) {
  Object.defineProperty(Object, "assign", {
    enumerable: false,
    configurable: true,
    writable: true,
    value: function(target, firstSource) {
      "use strict";
      if (target === undefined || target === null)
        throw new TypeError("Cannot convert first argument to object");
      var to = Object(target);
      for (var i = 1; i < arguments.length; i++) {
        var nextSource = arguments[i];
        if (nextSource === undefined || nextSource === null) continue;
        var keysArray = Object.keys(Object(nextSource));
        for (var nextIndex = 0, len = keysArray.length; nextIndex < len; nextIndex++) {
          var nextKey = keysArray[nextIndex];
          var desc = Object.getOwnPropertyDescriptor(nextSource, nextKey);
          if (desc !== undefined && desc.enumerable) to[nextKey] = nextSource[nextKey];
        }
      }
      return to;
    }
  });
}