http://toys.usvsth3m.com/javascript-under-pressure/ solutions

solutions.js

function doubleInteger(i) {
    // i will be an integer. Double it and return it.
    return i*2;
    
}

function isNumberEven(i) {
    // i will be an integer. Return true if it's even, and false if it isn't.
    return i%2 === 0;
}

function getFileExtension(i) {
    
    // i will be a string, but it may not have a file extension.
    // return the file extension (with no period) if it has one, otherwise false
    return i.split('.')[1] || false;
    
}

function longestString(i) {
    
    // i will be an array.
    // return the longest string in the array
    
    var str = '', j = 0;
    for(; j < i.length; j++) {
        if (typeof i[j] === 'string' && i[j].length > str.length) {
            str = i[j];
        }
    }
    return str;
    
}

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, j = 0;
    for(; j < i.length; j++) {
        if(typeof i[j] === 'number') {
            sum += i[j];
        } else {
            sum += Object.prototype.toString.call(i[j]) === '[object Array]' ? arraySum(i[j]) : 0;
        }
    }
    return sum;
}

Btw, u can't argue mine is more readable :P

also. getFileExtension("mylib.min.js") fail.

Under pressure, my OS allows just one .

in 86 chars, fixes most usecases for file extension:

function f(n,d,r){return r=!1,d='.',n.indexOf(d)!==-1&&(r=n.split(d).pop()),r}

fails on things like f('foo.'); or f('i like triangles. and model trains');