cripple.js is a small script designed to cripple the Javascript capabilities of your browser, rendering akin to an IE8 (see http://kangax.github.com/es5-compat-table/) browser.
To use it simply, include it in your test application / page prior to running application logic:
<script src="https://raw.github.com/DamonOehlman/cripple.js/master/cripple.js"></script>Because I still keep getting caught using particular varieties of JS goodness and stupidly forgetting that I have to support IE8. Using this script prevents me having to fire up a clunky old laptop to check for JS errors. CSS + Page Layout, well that's another thing entirely.
Have a look at including es5-shim into your page or compiled application code.