Plain JavaScript versus jQuery

Even a task as simple as this can be complicated without jQuery at our disposal. In plain JavaScript, we could add the highlight class in this way:

window.onload = function() {
  var divs = document.getElementsByTagName('div');
  for (var i = 0; i < divs.length; i++) {
    if (hasClass(divs[i], 'poem-stanza')
      && !hasClass(divs[i], 'highlight')) {
      divs[i].className += ' highlight';
    }
  }

  function hasClass( elem, cls ) {
    var reClass = new RegExp(' ' + cls + ' ');
    return reClass.test(' ' + elem.className + ' ');
  }
};

Listing 1.3

Despite its length, this solution does not handle many of the situations that jQuery takes care of for us in Listing 1.2, such as:

• Properly respecting other window.onload event handlers

• Acting as soon as the DOM is ready

• Optimizing element retrieval and other tasks with modern DOM methods

We can see that our jQuery-driven code is easier to write, simpler to read, and faster to execute than its plain JavaScript equivalent.