Difference between call and apply in JavaScript

 Here's the main difference - do you know the number of arguments beforehand?

1) Use apply if you don't know the number of arguments you will be passing, (or if they are already in an array or array-like object).

2) Use call otherwise, since there's no need to wrap the arguments in an array.

f.call(thisObject, a, b, c); // Fixed number of arguments

f.apply(thisObject, arguments); // Forward arguments

var args = [];
while (...) {
    args.push(some_value());
}
f.apply(thisObject, args); // Unknown number of arguments