How to add a new object (key-value pair) to an array in javascript?

.push() will add elements to the end of an array.

Use .unshift() if need to add some element to the beginning of array i.e:

items.unshift({'id':5});

Demo:

items = [{'id': 1}, {'id': 2}, {'id': 3}, {'id': 4}];
items.unshift({'id': 0});
console.log(items);

And use .splice() in case you want to add object at a particular index i.e:

items.splice(2, 0, {'id':5});
           // ^ Given object will be placed at index 2...

Demo:

items = [{'id': 1}, {'id': 2}, {'id': 3}, {'id': 4}];
items.splice(2, 0, {'id': 2.5});
console.log(items);

Use .push:

items.push({'id':5});

New solution with ES6

Default object

object = [{'id': 1}, {'id': 2}, {'id': 3}, {'id': 4}];

Another object

object =  {'id': 5};

Object assign ES6

resultObject = {...obj, ...newobj};

Result

[{'id': 1}, {'id': 2}, {'id': 3}, {'id': 4}, {'id': 5}];

Sometimes .concat() is better than .push() since .concat() returns the new array whereas .push() returns the length of the array.

Therefore, if you are setting a variable equal to the result, use .concat().

items = [{'id': 1}, {'id': 2}, {'id': 3}, {'id': 4}];
newArray = items.push({'id':5})

In this case, newArray will return 5 (the length of the array).

newArray = items.concat({'id': 5})

However, here newArray will return [{'id': 1}, {'id': 2}, {'id': 3}, {'id': 4}, {'id': 5}].

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