Javascript check yield support

Question

I read about the yield keyword in JavaScript and I need to use it in my project. I read that this keyword has been implemented starting from a certain version of JS so I think that old browsers don't support it (right?).

Is there a way to check if the yield keyword is supported? or at least is there a way to check if the version of JS is greater or equal than the one that implements that keyword (1.7)?

Answer 1

Here's a function for checking if yield can be used.

var can_yield = (function(){ 
    try { 
        return eval("!!Function('yield true;')().next()"); 
    } 
    catch(e) { 
        return false; 
    } 
})();

Answer 2

yield introduces new syntax to JavaScript. You won't be able to use yield unless you have specified that you want the new JavaScript syntax, by including a version number in the script type attribute(*).

When you specify a script version, only browsers that support the given version will execute the block at all. So only Firefox, and not IE, Opera or WebKit, will execute the top block in:

<script type="text/javascript;version=1.7">
    function x() {
        yield 0;
    }
    var canyield= true;
</script>
<script type="text/javascript">
    if (!window.canyield) {
        // do some fallback for other browsers
    }
</script>

(*: note that the type and version specified in the type attribute exclusively determines whether external scripts are fetched, executed, and the mode for the execution. The Content-Type of a script is, unfortunately, completely ignored.)