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

Either obj['key3'] = value3 or obj.key3 = value3 will add the new pair to the obj.

However, I know jQuery was not mentioned, but if you're using it, you can add the object through $.extend(obj,{key3: 'value3'}). E.g.:

var obj = {key1: 'value1', key2: 'value2'};
$('#ini').append(JSON.stringify(obj));

$.extend(obj,{key3: 'value3'});

$('#ext').append(JSON.stringify(obj));

Initial: 
Extended: 

jQuery.extend(target[,object1][,objectN]) merges the contents of two or more objects together into the first object.

And it also allows recursive adds/modifications with $.extend(true,object1,object2);:

var object1 = {
  apple: 0,
  banana: { weight: 52, price: 100 },
  cherry: 97
};
var object2 = {
  banana: { price: 200 },
  durian: 100
};
$("#ini").append(JSON.stringify(object1));    

$.extend( true, object1, object2 );
 
$("#ext").append(JSON.stringify(object1));

Initial: 
Extended: