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 = {}; 

Answer 1

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.

Answer 2

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");