对象的映射函数（而不是数组） [英] map function for objects (instead of arrays)

问题描述

我有一个对象：

I have an object:

myObject = { 'a': 1, 'b': 2, 'c': 3 }

我正在寻找一个本地方法，类似于 Array。 prototype.map ，它的用法如下：

I am looking for a native method, similar to Array.prototype.map that would be used as follows:

newObject = myObject.map(function (value, label) {
    return value * value;
});

// newObject is now { 'a': 1, 'b': 4, 'c': 9 }

JavaScript是否具有对象的这种 map 函数？ （我想要Node.JS，所以我不在乎跨浏览器的问题。）

Does JavaScript have such a map function for objects? (I want this for Node.JS, so I don't care about cross-browser issues.)

推荐答案

没有原生的 map 到 Object 对象，但是这样做如何：

There is no native map to the Object object, but how about this:

Object.keys(myObject).map(function(key, index) {
   myObject[key] *= 2;
});

console.log(myObject);

// => { 'a': 2, 'b': 4, 'c': 6 }

可以使用来... 中的对象：

But you could easily iterate over an object using for ... in:

for(var key in myObject) {
    if(myObject.hasOwnProperty(key)) {
        myObject[key] *= 2;
    }
}

更新

很多人都提到前面的方法不会返回一个新的对象，而是对对象本身进行操作。对于这个问题，我想添加另一个解决方案，返回一个新的对象，并保留原来的对象：

A lot of people are mentioning that the previous methods do not return a new object, but rather operate on the object itself. For that matter I wanted to add another solution that returns a new object and leaves the original object as it is:

var newObject = Object.keys(myObject).reduce(function(previous, current) {
    previous[current] = myObject[current] * myObject[current];
    return previous;
}, {});

console.log(newObject);
// => { 'a': 1, 'b': 4, 'c': 9 }

console.log(myObject);
// => { 'a': 1, 'b': 2, 'c': 3 }

Array.prototype.reduce code> 通过将前一个值与当前值进行某种合并来将数组减少为单个值。链由空对象 {} 初始化。在每次迭代时，都会添加一个新的 myObject 键，并将其平方作为值。

Array.prototype.reduce reduces an array to a single value by somewhat merging the previous value with the current. The chain is initialized by an empty object {}. On every iteration a new key of myObject is added with its square as value.

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