JavaScript - 如何遍历对象数组以创建一个新对象，其键是原始对象的初始键/值对的值

Question

Here is my situation:

I have to implement a function "mapById", which, when given an array of objects, returns an object, where the keys are the ids of the input objects and the values are the corresponding input objects.

var input = [{id: 102, name: "Alice"},
             {id: 205, name: "Bob", title: "Dr."},
             {id: 592, name: "Claire", age: 32}];

console.log(mapById(input));

should give the result below:

102: {id: 102, name: "Alice"},
205: {id: 205, name: "Bob", title: "Dr."},
592: {id: 592, name: "Claire", age: 32}

Here is my function thus far:

function mapById(list) {
    var obj = {};
    var objectKey = '';
    list.forEach(function(item) {
        objectKey = (Object.values(item)[0]);
        var obj = {[objectKey]: item};
    });
    return obj;
}

I can get a new key/value pair for each object in the original array but I can't figure out how to add each new key/value pair to the new object.

ObjectKey: 102
item: { id: 102, name: 'Alice' }
obj: { '102': { id: 102, name: 'Alice' } }
ObjectKey: 205
item: { id: 205, name: 'Bob', title: 'Dr.' }
obj: { '205': { id: 205, name: 'Bob', title: 'Dr.' } }
ObjectKey: 592
item: { id: 592, name: 'Claire', age: 32 }
obj: { '592': { id: 592, name: 'Claire', age: 32 } }

How can i fix this? If this was an array I could use the 'push' method. Is there a similar method for objects? Do I need a closure? I know this is basic stuff but I'm quite new to javascript.

Thanks.

Answer 1

You are actually quite close:

function mapById(list) {
    var obj = {};
    list.forEach(function(item) {
        obj[item.id] = item;
    });
    return obj;
}

How i would do that:

 const result = Object.assign(...input.map(el => ({[el.id] : el})));

Answer 2

Use Array.prototype.reduce() :

 var input = [{id: 102, name: "Alice"}, {id: 205, name: "Bob", title: "Dr."}, {id: 592, name: "Claire", age: 32}] var output = input.reduce(function(accumulator, item) { accumulator[item.id] = item return accumulator }, {}) console.log(output) 

Answer 3

var output = input.reduce(function(m,x,i) {
  m[x.id] = x
  return m
}, {})

The reduce function allows you to build a single object as you iterate an array. Notice the last parameter {} which initialises m to an empty object.