How to count JavaScript array objects?

Question

When I have a JavaScript object like this:

var member = {
    "mother": {
        "name" : "Mary",
        "age" : "48"
    },
    "father": {
        "name" : "Bill",
        "age" : "50"
    },
    "brother": {
        "name" : "Alex",
        "age" : "28"
    }
}

How to count objects in this object?!
I mean how to get a counting result 3, because there're only 3 objects inside: mother, father, brother?!

If it's not an array, so how to convert it into JSON array?

Solution 1

That's not an array, is an object literal, you should iterate over the own properties of the object and count them, e.g.:

function objectLength(obj) {
  var result = 0;
  for(var prop in obj) {
    if (obj.hasOwnProperty(prop)) {
    // or Object.prototype.hasOwnProperty.call(obj, prop)
      result++;
    }
  }
  return result;
}

objectLength(member); // for your example, 3

The hasOwnProperty method should be used to avoid iterating over inherited properties, e.g.

var obj = {};
typeof obj.toString; // "function"
obj.hasOwnProperty('toString'); // false, since it's inherited

Solution 2

You can try this code, it works perfectly in a browser:

Object.keys(member).length;

Solution 3

If you are using jquery on your page, this will work:

$(member).toArray().length;

Solution 4

You can use the Object.keys() method that returns an array of a given object's own enumerable properties:

Object.keys(member).length;

Solution 5

That is not an array, it is an object literal.

You can iterate the objects properties and count how many it owns:

var count = 0;
for (var k in obj) {
  // if the object has this property and it isn't a property
  // further up the prototype chain
  if (obj.hasOwnProperty(k)) count++;
}

View more solutions

Comments

[James]

Might be worth checking for Mozilla's __count__ property before iterating over the object...

[Christian C. Salvadó]

@J-P: __count__ is marked as obsolete for Gecko 1.9.3, (in Gecko 1.9.3a5pre, (Firefox 3.7a5pre) it doesn't exist anymore)

[Christian C. Salvadó]

@J-P, something that you could check before iterating, is the existence of the new ECMAScript 5th Edition Object.keys method, ES5 is starting to be implemented by all major browser vendors, something like this: if (typeof Object.keys === "function") return Object.keys(obj).length;

[Frederico]

I feel like this is overdoing. If he's simply counting the number of properties in a JSON, relying on Object.keys(memebers) should be enough.

[Dale K]

Seems identical to an earlier answer.

[J A S K I E R]

Finally the solution for "Inside" methods, instead of documentation for Querries)