javascript under pressure

gistfile1.js

//01. i will be an integer. Double it and return it.
function doubleInteger(i) {
    return i*2;
}

//02. i will be an integer. Return true if it's even, and false if it isn't.
function isNumberEven(i) {
    return (i%2 == 0);
    
}

//03. 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
function getFileExtension(i) {
    if(i.indexOf('.')==-1){
        return false
    }else{
        return i.split('.')[1];
    }
    
}

//04. i will be an array. return the longest string in the array
function longestString(i) {
    var arr=Array();
    for(var j=0;j<i.length;j++){
        if(typeof i[j] ==='string'){
            arr.push(i[j]);
        }
    }
    return arr.sort(function (a, b) { return b.length - a.length; })[0];
}

//05 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.
function arraySum(i) {
    sum=0;
    for(var j=0;j<i.length;j++){
        if(typeof i[j]==='number'){
            sum+=parseInt(i[j]);
        }else{
            if(Array.isArray(i[j])){
                sum+=parseInt(arraySum(i[j]));
            }
        }
    }
    return sum;
}