Why doesn’t deleting from a Javascript array change its length?

Question

I have an array:

data.Dealer.car[0]
data.Dealer.car[1]
data.Dealer.car[2]

If I do this:

alert(data.Dealer.car.length);
delete data.Dealer.car[1];
alert(data.Dealer.car.length);

It gives me the same count each time. Does the removed element still exist?

Answer 1

If you want to remove an item, use the splice method:

alert(data.Dealer.car.length);
data.Dealer.car.splice(1, 1);
alert(data.Dealer.car.length);

But notice that the indices have changed.

Answer 2

JavaScript arrays aren't sparse, if you have a 0 and a 2, then element 1 must exist. Meaning the length is going to be 3.

Answer 3

Building on what @Ray Hidayat posted:

JavaScript arrays are sparse. If you have an array of length 3, deleting the reference at [1] will simply "unset" that item, not remove it from the array, or update that array's length. You could accomplish the same with

myArray = [0, , 2, , , , ];  // length 6; last three items undefined

Here's a Fiddle: http://jsfiddle.net/WYKDz/

NOTE: removing items from the middle of large arrays can be computationally intensive. See this post for more info: Fastest way to delete one entry from the middle of Array()

Answer 4

Array.shift() would remove the first item from the array and make it shorter. Array.pop() will remove the last item.

Answer 5

I think you're looking for this:

var arr = [0,1,2,3,4];

alert( arr.splice( 2, 1 ) ); // alerts 2, the element you're removing
alert( arr ) // alerts 0,1,3,4  - the remaining elements

here's a MDC reference

Answer 6

Ok.. fixed this now as the array was still allocated.

I needed to basically do:

var newCar = new Array();
for (i = 0 ; i < tblSize -2; i ++)
{
    newCar[i]=data.Dealer.car[i];
}
data.Dealer.car = newCar;