How do I check if an array includes a value in JavaScript

Question

What is the shortest and most efficient technique to determine whether a JavaScript array has a value?

This is the only method I know:

function contains(a, obj) {
    for (var i = 0; i < a.length; i++) {
        if (a[i] === obj) {
            return true;
        }
    }
    return false;
}

Is there a more efficient and succinct method to achieve this?