The jList property of the object is just a string, so you need to convert it to a Javascript object using JSON.parse().

// Dummy of your "data" variable
var data = {"jList":"[{\"added_by\":\"Ani\",\"description\":\"example description.\",\"start_date \":\"2014-10-10\",\"mark\":255,\"id\":975},{\"added_by\":\"Ani\",\"description \":\"example description..\",\"start_date\":\"2014-10-10\",\"mark\":255,\"id\":980 }]"};

var myList = JSON.parse(data.jList);
alert(myList.length); // Alerts "2"

See this fiddle: https://jsfiddle.net/x983vvr6/2/

Essentially, assuming you have correctly set up the object you simply need to call

OrderStatusArray.length

And it will display the length of the array.

What length are you expecting? 3 is the correct answer and the answer which this fiddle shows.

Full code:

var OrderStatusArray = [{
"orderStatus": "S",
    "x_ExtnIsModifiable": "N",
    "grandTotal": "24",
    "orderId": "",
    "grandTotalCurrency": "USD",
    "placedDate": "2015-05-11T17:56:27.406Z",
    "x_ExtnIsModifiableUntil": "2012-07-24 23:59:00.0",
    "externalOrderID": "29001e"
  }, {
"orderStatus": "S",
    "x_ExtnIsModifiable": "N",
    "grandTotal": "23",
    "orderId": "",
    "grandTotalCurrency": "USD",
    "placedDate": "2015-04-11T17:56:27.406Z",
    "x_ExtnIsModifiableUntil": "2012-07-24 23:59:00.0",
    "externalOrderID": "29001d"
   }, {
"orderStatus": "S",
    "x_ExtnIsModifiable": "N",
    "grandTotal": "22",
    "orderId": "",
    "grandTotalCurrency": "USD",
    "placedDate": "2015-03-11T17:56:27.406Z",
    "x_ExtnIsModifiableUntil": "2012-07-24 23:59:00.0",
    "externalOrderID": "29001c"
     }];


console.log("Your order length array is: " + OrderStatusArray.length);

The variable you are trying to store is already a json encoded string. You can not stringify it again.

You can drop those ' and reformat the json, then it would be a normal json, then you can call stringify on it.

var data = {"history":[{"keyword":key,"msg":msg,"ver":ver}]};
localStorage.setItem("history", JSON.stringify(data));

To get the length of the array after retrieve:

var historydata = JSON.parse(localStorage.getItem("history"));
console.log(historydata.history.length);

.length is a special property in Javascript arrays, which is defined as "the biggest numeric index in the array plus one" (or 2^32-1, whatever comes first). It's not "the number of elements", as the name might suggest.

When you iterate an array, either directly with for..of or map, or indirectly with e.g. JSON.stringify, JS just loops over all numbers from 0 to length - 1, and, if there's a property under this number, outputs/returns it. It doesn't look into other properties.

Objects don't have a .length property.

A simple solution if you know you don't have to worry about hasOwnProperty checks, would be to do this:

Object.keys(data).length;

If you have to support IE 8 or lower, you'll have to use a loop, instead:

var length= 0;
for(var key in data) {
    if(data.hasOwnProperty(key)){
        length++;
    }
}

JavaScript doesn't have a .length property for objects. If you want to work it out, you have to manually iterate through the object.

function objLength(obj){
  var i=0;
  for (var x in obj){
    if(obj.hasOwnProperty(x)){
      i++;
    }
  } 
  return i;
}


alert(objLength(JSONObject)); //returns 4

Edit:

Javascript has moved on since this was originally written, IE8 is irrelevant enough that you should feel safe in using Object.keys(JSONObject).length instead. Much cleaner.

Its not an array you need to parse it first to get as an array :

var ownAc=JSON.parse(user.ownAccount)
console.log(ownAc.length);

This does the same think as Object.keys(obj).length, but without the browser compatibility issue (I think).

What about:

var obj = {
    yo: {
         a: 'foo',
         b: 'bar'
    }
    hi: {
        c: 'hello',
        d: 'world',
        e: 'json'
    }
}

var arr = [], len;

for(key in obj) {
    arr.push(key);
}

len = arr.length;

console.log(len) //2

OR

var arr = [], len;

for(key in obj.hi) {
    arr.push(key);
}

len = arr.length;

console.log(len) //3

OR, in your case

var arr = [], len;

for(key in studentMockBeanMap) {
    arr.push(key);
} 

len = arr.length;

console.log(len); //4

Before going to answer read this Documentation once. Then you clearly understand the answer.

Try this It may work for you.

Object.keys(data.shareInfo[i]).length

your data is already json format:do like this

var App = [
           {
             "id": "123",
             "caption": "Test",
             "description": "Test Desc"
           },
           {
             "id": "345",
             "caption": "adsasdasd",
             "description": ""
           },
           {
             "id": "456",
             "caption": "adsasdasd",
             "description": ""
           },
           {
             "id": "578",
             "caption": "adsasdasd",
             "description": ""
           }
          ];

console.log(App);
console.log(App[0].length);// you can not get length from this because it is not array it's an object now.

var AppLen = App.length;
alert(AppLen);

That's because categoryData is not an Array - it's an Object. And while some JS objects (arguments, for example) support length property, those created with object literal notation do not.

You can count your object's length by yourself, with this:

function countProps(obj) {
    var count = 0;
    for (var p in obj) {
      obj.hasOwnProperty(p) && count++;
    }
    return count; 
}

This can be done even in a more simple way, if your target environment supports (or has it shimmed) the Object.keys method:

function sizeObj(obj) {
  return Object.keys(obj).length;
}

... and that's exactly how it's done in Underscore.js library method:

_.size = function(obj) {
    if (obj == null) return 0;
    return (obj.length === +obj.length) ? obj.length : _.keys(obj).length;
};

You can use something like this

var myObject = {'name':'Kasun', 'address':'columbo','age': '29'}

var count = Object.keys(myObject).length;
console.log(count);

Try this, there is a correction in your code. You're not pushing IDs into an array but you're assigning a new value of IDs every time.

it('gets person id in array',()=>{
  let array_ids =[];
  let count=0;
    return response.then((api_response)=>{
     for(var i=1;i<api_response.body.length;i++){
       //this is correctly printing the person id of response
       console.log('Person ids are ==>'+api_response.body[i].person_id);
       count++;

       //this is not working
       array_ids.push(api_response.body[i].person_id); //update
}
      console.log('Count is '+count) //prints correct number
      console.log('Array length '+array_ids.length) //prints incorrect length - sometimes 11, sometimes 12
});
});

You should do something like:

$.getJSON('fresh_posts.php',function(data){
    global_save_json = data.freshcomments;
    var countPosts = Object.keys(data.freshposts).length;
});

I think you have a misunderstanding of what JSON is. JSON is a string and not an object hence it's abbreviation of JavaScript Object Notation. What you want is colloquially referred to as a POJO or Plain Old Javascript Object. They are different.

It seems like whatever you are using to make the HTTP request is auto parsing the JSON response into a POJO on some browsers and not on others.

var json = '[{"url":"http://google.com"},{"url":"http://yahoo.com"}]';
json.length // 56 (this is the character count since json is a string)
var obj = JSON.parse(json);
obj.length // 2 (since there are two items in the array
obj[0].url // 'http://google.com'

UPDATE: after discussion with OP, his issue was lack of support for responseType in his XMLHttpRequest handler (it's a level 2 enhancement where as the browsers in question only support level 1). Added the following check to see if the response was auto-parsed to an object and if not do it manually:

var obj = typeof xhr.response === 'string' ? JSON.parse(xhr.response) : xhr.response;

Your JSON is not an array, but an object. If you want it to be an array, it should be something like this:

[
  "{\"start\":{\"lat\":22.9939202,\"lng\":72.50009499999999},\"end\":{\"lat\":23.0394491,\"lng\":72.51248850000002},\"waypoints\":[[23.0316834,72.4779436]]}",

  "{\"start\":{\"lat\":22.9999061,\"lng\":72.65318300000001},\"end\":{\"lat\":23.0420584,\"lng\":72.67145549999998},\"waypoints\":[[23.02237,72.6500747]]}",

  "{\"start\":{\"lat\":23.0394491,\"lng\":72.51248850000002},\"end\":{\"lat\":22.9999061,\"lng\":72.65318300000001},\"waypoints\":[[23.0016629,72.58898380000005]]}"

 ]

Then, you can get a javascript array as follows:

var array = JSON.parse(jax.responseText);

And access values as follows:

array[0]

array.length

EDIT: In order to have a real JSON array with the PHP json_encode method, see this related question.

With this modification you will be able to use all the possibilities of JS array without workaround.