Checking for a numerical index in a javascript array

Question

I'm receiving json data that is aggregated by numerical indexes.

When I'm in my forloop, for example, the index might start at 1, which means in my forloop an error would occur because 0 doesnt exist.

How do I check if a numerical index exists in the javascript array?

Answer 1

var a = [1, 2, 3], index = 2;

if ( a[index] !== void 0 ) { /* void 0 === undefined */
    /* See concern about ``undefined'' below.        */
    /* index doesn't point to an undefined item.     */
}