Javascript 1.7

JavaScript 1.7 is a language update introducing several new features, in particular generators, iterators, array comprehensions, let expressions, and destructuring assignment.

— MDN Javascript 1.7

In order to use some of the new features of JavaScript 1.7, you need to specify that you wish to use JavaScript 1.7

<script type="application/javascript;version=1.7">
//Your javascript 1.7 here
</script>