Throttles execution of any given function - without initial delays

throttle.js

/**
 * Throttles execution of given function
 * @param {function} func - function to execute
 * @param {number} delay - delay in milisecionds
 * @param {object} scope - optional scope in which function will be executed
 */
 var throttle = function(func, delay, scope) {
   var delay = delay || 500;
   var scope = scope || this;
   var busy  = false;
   
   return function() {
     if (busy) { return; }
     busy = true;
     setTimeout(function() { busy = false; }, delay);
     func.apply(scope, [].slice.apply(arguments));
  };
};

/**
 * Test & usage example
 */
var test;
var action = throttle(function(arg) { test = arg; }, 500);

action('TEST 1!');
console.log(test); // 'TEST 1!'

action('TEST 2!');
console.log(test); // 'TEST 1!'

setTimeout(function() {
  action('TEST 3!');
  console.log(test); // 'TEST 3!'
}, 501);

action('TEST 4!');
console.log(test); // 'TEST 1!'