Throttle Function Implementation

Write a function that accepts a function and timeout, x, in number of milliseconds. It returns a function that can only be executed once per x milliseconds. This can be useful for limiting the number of time and computation heavy function that are run. For example, making AJAX requests to an autocompletion API.

Once written, add a third parameter that will allow the function to be executed immediately if set to true. Otherwise the function will run at the end of the timeout period.

module.exports = function (fn, delay, execAsap) {
  var timeout; // Keeps a reference to the timeout inside the returned function

  return function () {
    // Continue to pass through the function execution context and arguments
    var that = this,
        args = arguments;

    // If there is no timeout variable set, proceed to create a new timeout
    if (!timeout) {
      execAsap && fn.apply(that, args);

      timeout = setTimeout(function () {
        execAsap || fn.apply(that, args);
        // Remove the old timeout variable so the function can run again
        timeout = null;
      }, delay || 100);
    }
  };
};