Find length (size) of an array in jquery

Question

I think I'm going crazy. I have a simply question that I'm struggling with for some reason.

Why does the below return 'undefined'?

var testvar={}; testvar[1]=2; testvar[2]=3; alert(testvar.length); 

edit I originally typed testvar[1].length. I knew this to be an error. I meant testvar.length

Answer 1

Because 2 isn't an array, it's a number. Numbers have no length.

Perhaps you meant to write testvar.length; this is also undefined, since objects (created using the { ... } notation) do not have a length.

Only arrays have a length property:

var testvar = [  ]; testvar[1] = 2; testvar[2] = 3; alert(testvar.length);    // 3 

Note that Javascript arrays are indexed starting at 0 and are not necessarily sparse (hence why the result is 3 and not 2 -- see this answer for an explanation of when the array will be sparse and when it won't).

Answer 2

testvar[1] is the value of that array index, which is the number 2. Numbers don't have a length property, and you're checking for 2.length which is undefined. If you want the length of the array just check testvar.length