How to get the number of elements in a JSON array?

I'm getting json_encode data from controller. The resulting array is like:

[
  { "name": "aaa" },
  { "name": "bbb" },
  { "name": "ccc" }
]

How to get the number of elements in this array using JavaScript?

You can always get array length by length property of an array.

Here is the reference from w3school:
http://www.w3schools.com/jsref/jsref_length_array.asp

Code:

function myFunction() {
  var fruits = ["Banana", "Orange", "Apple", "Mango"];
  document.getElementById("demo").innerHTML = fruits.length;
}

<p>Click the button to create an array, then display its length.</p>
<button onclick="myFunction()">Try it</button>
<p id="demo"></p>

Try the working code in fiddle:
http://jsfiddle.net/5arrc15d/