Delay responses to events

event-with-delay.js

/*
 * Sometimes it's useful to wait for the user to complete the action
 * he's engaged on instead of trying to handle it right away. A practical
 * example is to avoid flooding servers with tons of autocompletion requests
 * for each key stroke the user types in. A more efficient approach is to wait
 * until the user feeds enough before attempting make requests for only one or
 * two letters.
 *
 * Usage:
 * listenToEventAndDelay(textInput, 'keydown', autoCompleteFunction, 500);
 */
 
function listenToEventAndDelay(subject, eventName, callback, delay) {
  var timeout;
  subject.addEventListener(eventName, function (e) {
    if (timeout) {
      clearTimeout(timeout);
    }
    timeout = setTimeout(function () {
      timeout = null;
      callback(e)
    }, delay);
  });
}