What browsers currently support JavaScript's 'let' keyword?

firefox, firefox3.6, javascript

Solution

EDIT: `let` and `const` are supported by all modern browsers and are part of the ECMAScript 2015 (ES6) specification.

Basically if you don't need to support anything below IE11, `let` and `const` are safe to use nowadays.

On IE11 there's a small quirk with `let` when used with `for` loops, the variable is not bound to the `for` block as you would expect, it behaves as `var` did...

See also: let and const support.

Old and outdated answer from 2010: Those extensions are not ECMA-Standard, they are supported only by the Mozilla implementation.

On browser environments you should include the JavaScript version number in your `script` tag to use it:

<script type="application/javascript;version=1.7">  
  var x = 5;
  var y = 0;

  let (x = x+10, y = 12) {
    alert(x+y + "\n");
  }

  alert((x + y) + "\n");
</script>

Problem

I'm developing an app and don't have to ever worry about Internet Explorer and was looking into some of the features present in A+ grade browsers that aren't in Internet Explorer1. One of these features I wanted to play around with is JavaScript's let keyword I can't seem to get any of their 'let' examples to work in Firefox 3.6 (User-Agent string: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2) Gecko/20100115 Firefox/3.6 (.NET CLR 3.5.30729)). I get `SyntaxError: missing ; before statement` when executing `let foo = "bar"`. So, what browsers support the let keyword? (Or am I doing something wrong?)

Original source