Demonstrates how to create a theme function in javascript.

Drupal: Javascript theme function

(function ($) {
  // Declare the theme function.
  Drupal.theme.prototype.projectTeaser = function(image_url, title, url) {
    return '<div class="teaser"><img class="teaser--image" src="' + image_url + '" /><h2 class="teaser--title">' + title + '</h2><a class="teaser--link" href="' + url +'">View Project</a>';
  }
  
  Drupal.behaviors.gtpePurchaseOrder = {
    attach: function (context, settings) {
      // Call the theme function like so. It should return themed markup.
      var teaser = Drupal.theme('projectTeaser', 'http://placehold.it/300x300', 'I did this fancy stuff', 'http://npr.org');
      
      // Append it to a div.
      $('.project-teaser').append(teaser);
    }
  }
})(jQuery);