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

Loop stops when found first duplicate:

function has_duplicates(arr) {

    var x = {}, len = arr.length;
    for (var i = 0; i < len; i++) {
        if (x[arr[i]]) {
             return true;
        }
        x[arr[i]] = true;
    }
    return false;

}

Edit (fix 'toString' issue):

function has_duplicates(arr) {

    var x = {}, len = arr.length;
    for (var i = 0; i < len; i++) {
        if (x[arr[i]] === true) {
             return true;
        }
        x[arr[i]] = true;
    }
    return false;

}

this will correct for case has_duplicates(['toString']); etc..