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

You can create a new object by using the {[key]: value} syntax:

const foo = {
  a: 'key',
  b: 'value'
}

const bar = {
  [foo.a]: foo.b
}

console.log(bar); // {key: 'value'}
console.log(bar.key); // value

const baz = {
  ['key2']: 'value2'
}

console.log(baz); // {key2: 'value2'}
console.log(baz.key2); // value2

With the previous syntax you can now use the spread syntax {...foo, ...bar} to add a new object without mutating your old value:

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

const bar = {...foo, ...{['c']: 3}};

console.log(bar); // {a: 1, b: 2, c: 3}
console.log(bar.c); // 3