Why is JSONObject.length undefined? [closed]

Question

In the code below, JSONObject.length is 2:

var JSONObject = [{
    "name": "John Johnson",
    "street": "Oslo West 16",
    "age": 33,
    "phone": "555 1234567"
}, {
    "name": "John Johnson",
    "street": "Oslo West 16",
    "age": 33,
    "phone": "555 1234567"
}];

However, in the code below, JSONObject.length is undefined. Why?

var JSONObject = {
    "name": "John Johnson",
    "street": "Oslo West 16",
    "age": 33,
    "phone": "555 1234567"
};

Answer 1

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.

Answer 2

The following is actually an array of JSON objects :

var JSONObject = [{ "name":"John Johnson", "street":"Oslo West 16", "age":33,
"phone":"555 1234567"}, {"name":"John Johnson", "street":"Oslo West 16", 
"age":33, "phone":"555 1234567" }];

So, in JavaScript length is a property of an array. And in your second case i.e.

var JSONObject = {"name":"John Johnson", "street":"Oslo West 16", "age":33, 
"phone":"555 1234567"};

the JSON object is not an array. So the length property is not available and will be undefined. So you can make it as an array as follows:

var JSONObject = [{"name":"John Johnson", "street":"Oslo West 16", "age":33, 
"phone":"555 1234567"}];

Or if you already have object say JSONObject. You can try following:

var JSONObject = {"name":"John Johnson", "street":"Oslo West 16", "age":33, 
"phone":"555 1234567"};
var jsonObjArray = []; // = new Array();
jsonObjArray.push(JSONObject);

And you do get length property.