How can I add a key/value pair to a JavaScript object?

Question

Here is my object literal:

var obj = {key1: value1, key2: value2};

How can I add field key3 with value3 to the ob

Answer 1

Simply adding properties:

And we want to add prop2 : 2 to this object, these are the most convenient options:

1. Dot operator: object.prop2 = 2;
2. square brackets: object['prop2'] = 2;

So which one do we use then?

The dot operator is more clean syntax and should be used as a default (imo). However, the dot operator is not capable of adding dynamic keys to an object, which can be very useful in some cases. Here is an example:

const obj = {
  prop1: 1
}

const key = Math.random() > 0.5 ? 'key1' : 'key2';

obj[key] = 'this value has a dynamic key';

console.log(obj);

Merging objects:

When we want to merge the properties of 2 objects these are the most convenient options:

1. Object.assign(), takes a target object as an argument, and one or more source objects and will merge them together. For example:

const object1 = {
  a: 1,
  b: 2,
};

const object2 = Object.assign({
  c: 3,
  d: 4
}, object1);

console.log(object2);

2. Object spread operator ...

const obj = {
  prop1: 1,
  prop2: 2
}

const newObj = {
  ...obj,
  prop3: 3,
  prop4: 4
}

console.log(newObj);

Which one do we use?

• The spread syntax is less verbose and has should be used as a default imo. Don't forgot to transpile this syntax to syntax which is supported by all browsers because it is relatively new.
• Object.assign() is more dynamic because we have access to all objects which are passed in as arguments and can manipulate them before they get assigned to the new Object.