How do I build JSON dynamically in javascript?

Question

var myJSON = {  
              "list1" : [ "1", "2" ],
              "list2" : [ "a", "b" ],
              "list3" : [ { "key1" : "value1" }, { "key2" : "value2" } ],
              "not_a_list" : "11"
             };

How do I dynamically build this JSON structure in javascript? Google tells me to use use some push command, but I've only found specific cases. So what do I write to enter data to "listX" and "not_a_list". Appending as well as creating a new list. The whole procedure begninning with:

var myJSON = {};

Do you really mean JSON (which is string) or a collection of nest JavaScript objects, arrays, strings and numbers (that could be serialized to JSON)? — Quentin
– Quentin, Commented Nov 30, 2010 at 13:03

Neall · Accepted Answer · 2010-11-30 13:39:23Z

83

First, I think you're calling it the wrong thing. "JSON" stands for "JavaScript Object Notation" - it's just a specification for representing some data in a string that explicitly mimics JavaScript object (and array, string, number and boolean) literals. You're trying to build up a JavaScript object dynamically - so the word you're looking for is "object".

With that pedantry out of the way, I think that you're asking how to set object and array properties.

// make an empty object
var myObject = {};

// set the "list1" property to an array of strings
myObject.list1 = ['1', '2'];

// you can also access properties by string
myObject['list2'] = [];
// accessing arrays is the same, but the keys are numbers
myObject.list2[0] = 'a';
myObject['list2'][1] = 'b';

myObject.list3 = [];
// instead of placing properties at specific indices, you
// can push them on to the end
myObject.list3.push({});
// or unshift them on to the beginning
myObject.list3.unshift({});
myObject.list3[0]['key1'] = 'value1';
myObject.list3[1]['key2'] = 'value2';

myObject.not_a_list = '11';

That code will build up the object that you specified in your question (except that I call it myObject instead of myJSON). For more information on accessing properties, I recommend the Mozilla JavaScript Guide and the book JavaScript: The Good Parts.

answered Nov 30, 2010 at 13:39

Neall

27.3k5 gold badges51 silver badges48 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Kirill Bulygin Over a year ago

Regarding "the keys are numbers" (and being slightly pedantic): it's not quite so, keys are always strings in objects (including arrays), and [0] etc. implicitly transforms to ["0"] etc. (see, for example, developer.mozilla.org/en/docs/Web/JavaScript/Reference/…).

AndreKR · Accepted Answer · 2010-11-30 13:02:56Z

15

As myJSON is an object you can just set its properties, for example:

myJSON.list1 = ["1","2"];

If you dont know the name of the properties, you have to use the array access syntax:

myJSON['list'+listnum] = ["1","2"];

If you want to add an element to one of the properties, you can do;

myJSON.list1.push("3");

answered Nov 30, 2010 at 13:02

AndreKR

33.9k21 gold badges120 silver badges181 bronze badges

Collectives™ on Stack Overflow

How do I build JSON dynamically in javascript?

2 Answers 2

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related