fastest way to detect if duplicate entry exists in javascript array?

Question

var arr = [\'test0\',\'test2\',\'test0\'];

Like the above,there are two identical entries with value \"test0\",how to check it most efficiently?

Answer 1

This will do the job on any array and is probably about as optimized as possible for handling the general case (finding a duplicate in any possible array). For more specific cases (e.g. arrays containing only strings) you could do better than this.

function hasDuplicate(arr) {
    var i = arr.length, j, val;

    while (i--) {
        val = arr[i];
        j = i;
        while (j--) {
            if (arr[j] === val) {
                return true;
            }
        }
    }
    return false;
}