Quick little function for testing screensize against breakpoints. Requires jQuery.

breakpoint.js

    /**
     * Determines if screen size is within givin breakpoint.
     *
     * @param (string) op
     *   The breakpoint size to compare. Supported sizes are medium, large, xlarge
     *   and giant.
     *
     * @param (bool) mobileFirst
     *   Changes comparison from <= to >= if set to false. Deafults to true.
     *
     * @return (bool)
     */
    function breakPoint(op, mobileFirst) {
      if (typeof(mobileFirst) === 'undefined') mobileFirst = true;

      var breakPoints = {
        medium: 480,
        large: 640,
        xlarge: 960,
        giant: 1280,
      };

      if (mobileFirst) {
        return parseInt($(window).width()) >= breakPoints[op];
      }
      else {
        return parseInt($(window).width()) <= breakPoints[op];
      }
    }