Loading two versions of jQuery to support IE6-8 and modern browsers
jQuery 2.x offers several advantages over jQuery 1.x in that the code is smaller and there is some added functionality, but the downside is that jQuery 2.x doesn’t support Internet Explorer versions 6, 7 and 8.
To account for this and to ensure continued functionality on websites that need to support those older browsers, jQuery 1.10 is available. The jQuery team will keep both branches in development until a time when support for IE8 is no longer required. Scripts that rely upon jQuery 1.x should also work with jQuery 2.0.
Until the day that support for IE8 is no longer required, best practice is to implement both jQuery 1.10 and jQuery 2.x on websites in development. To do this, conditional comments are required:
<!--[if lt IE 9]> <script src="/path/to/jquery-1.10.x.js"></script> <![endif]--> <!--[if gte IE 9]><!--> <script src="/path/to/jquery-2.0.x.js"></script> <!--<![endif]-->
If it has been some time since the version of jQuery on your website has been updated, you may want to run jQuery Migrate.