I need to identify if my JSON feed has child key/value pairs and handle them differently. what i mean is:

{ 
    "dashboard" :[
    {
        "name": "",
        "image": "",
        "description":"",
        "linkurl":"" },

    {
        "name": "",
        "image": "",
        "description":"",
        "linkurl":""
        },
    "related" : [
    {
        "name": "",
        "image": "",
        "description":"",
        "linkurl":""
        },
    {
        "name": "",
        "image": "",
        "description":"",
        "linkurl":""
        }]
  ]

How do i identify that this JSON has those child ("related") key/value pairs?

I need to identify if my JSON feed has child key/value pairs and handle them differently. what i mean is:

{ 
    "dashboard" :[
    {
        "name": "",
        "image": "",
        "description":"",
        "linkurl":"" },

    {
        "name": "",
        "image": "",
        "description":"",
        "linkurl":""
        },
    "related" : [
    {
        "name": "",
        "image": "",
        "description":"",
        "linkurl":""
        },
    {
        "name": "",
        "image": "",
        "description":"",
        "linkurl":""
        }]
  ]

How do i identify that this JSON has those child ("related") key/value pairs?

• javascript
• jquery
• json

• 3 jsonlint. Your JSON is mal-formed – timdream Commented Aug 18, 2011 at 7:54

2 Answers 2

After parsing the JSON string into a JavaScript object (see greengit's answer), you have three options:

• typeof obj.related !== 'undefined'
• obj.related !== undefined. Be careful when using the undefined variable, it can be changed by other scripts. If you are using it, make sure to wrap your code in anonymous function that sets it to a correct value - see Javascript Garden about that, under "Handling Changes to the Value of undefined"
• 'related' in obj

IIRC, using in should be the fastest

update I remember it the other way around - in is the slowest way of doing that, by a large margin (98%!). Also, using typeof obj.key !== 'undefined' is much faster than obj.key !== undefined (the latter is 80% slower). See http://jsperf./in-vs-not-undefined.

Convert JSON into a JS object and see if what you want is undefined.

var obj = JSON.parse(json_string);

if ( obj.related == undefined ) {
  ...