map function for objects (instead of arrays)

Question

I have an object:

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

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 } 

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

Answer 1

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

var myObject = { 'a': 1, 'b': 2, 'c': 3 };    Object.keys(myObject).map(function(key, index) {    myObject[key] *= 2;  });    console.log(myObject);  // => { 'a': 2, 'b': 4, 'c': 6 }

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

var myObject = { 'a': 1, 'b': 2, 'c': 3 };    for (var key in myObject) {    if (myObject.hasOwnProperty(key)) {      myObject[key] *= 2;    }  }    console.log(myObject);  // { 'a': 2, 'b': 4, 'c': 6 }

Update

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 myObject = { 'a': 1, 'b': 2, 'c': 3 };    // returns a new object with the values at each key mapped using mapFn(value)  function objectMap(object, mapFn) {    return Object.keys(object).reduce(function(result, key) {      result[key] = mapFn(object[key])      return result    }, {})  }    var newObject = objectMap(myObject, function(value) {    return value * 2  })    console.log(newObject);  // => { 'a': 2, 'b': 4, 'c': 6 }    console.log(myObject);  // => { 'a': 1, 'b': 2, 'c': 3 }

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 twice the key as the value.

Update

With new ES6 features, there is a more elegant way to express objectMap.

const objectMap = (obj, fn) =>    Object.fromEntries(      Object.entries(obj).map(        ([k, v], i) => [k, fn(v, k, i)]      )    )      const myObject = { a: 1, b: 2, c: 3 }    console.log(objectMap(myObject, v => 2 * v))