Is setTimeout with no delay the same as executing the function instantly?

It won't necessarily run right away, neither will explicitly setting the delay to 0. The reason is that setTimeout removes the function from the execution queue and it will only be invoked after JavaScript has finished with the current execution queue.

console.log(1);
setTimeout(function() {console.log(2)});
console.log(3);
console.log(4);
console.log(5);
//console logs 1,3,4,5,2

for more details see http://javascriptweblog.wordpress.com/2010/06/28/understanding-javascript-timers/