"You Can't JavaScript Under Pressure" - LEVEL 5 - Closures + Recursion FTW! - http://toys.usvsth3m.com/javascript-under-pressure/

level5.js

function arraySum(i) {
    
    // i will be an array, containing integers, strings and/or arrays like itself.
    // Sum all the integers you find, anywhere in the nest of arrays.
    var sum = 0;
    
    function maybeSum(x) {
        if (typeof x === 'number') {
            sum += parseInt(x);
        } else if (Array.isArray(x)) {
            for (var j=0; j<x.length; j++) {
                maybeSum(x[j]);
            }
        }
    }
    
    // main cycle
    for (var k=0; k<i.length; k++) {
        maybeSum(i[k]);
    }
    return sum;
}