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)?
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.)
Strictly speaking, only Mozilla Browsers support JavaScript. All browsers should support ECMAScript and older versions of JavaScript are implementations of ECMAScript.
This site lists what versions of Javascript are supported on what versions of browser.
MSIE uses JScript. JScript does not have yield in it. Therefore, using yield will limit the browser support for your page.
Try https://developer.mozilla.org/en/New_in_JavaScript_1.7 for info on using JavaScript 1.7
I have spent a lot of time with yield recently, and bobince isn't completely wrong, but Chrome 31 does not interpret JavaScript version to 1.7 blocks, even with the Experimental JavaScript flag turned on (chrome://flags/#enable-javascript-harmony). Due to implementation differences between Chrome 31 and Firefox, Tymon Sturgeon's method is unable to detect yield in Chrome 31 with Experimental JS on, although it is very close. With a few modifications, it can detect the existence of yield for both Firefox and Chrome 31 with Experimental JS on.
First I'll quickly cover the yield differences (writing it the long way for clarity):
In Firefox:
var fooGen = function(){ yield 1; yield 2; };
var iterator = fooGen();
console.log(iterator.next()); // prints 1
console.log(iterator.next()); // prints 2
In Chrome 31 with Experimental JavaScript enabled:
// Note the *
var fooGen = function*(){ yield 1; yield 2; };
var iterator = fooGen();
console.log(iterator.next().value); // prints 1
console.log(iterator.next().value); // prints 2
.value is required in Chrome because it yields an object, but more importantly, the generator requires a "*" in the function definition. Also, I could not find a way to create a generator from the capital "F" Function: new Function('', '{yield 5;}'); in Chrome. If you know how, leave a comment below.
To properly detect yield in Firefox and Chrome, I have used a bit of code with some back and forth:
<script type="application/javascript">
var can_yield = (function(){
try {
// Assuming Chrome's generator syntax
var funcUsingYield = new Function('', '{ var interp = function* generator(){ yield true; }}');
return true;
} catch(e) {
return false;
}
})();
</script>
<script type="application/javascript;version=1.7">
// Redefine the `can_yield` function inside a JS1.7 block. Probably safe to simply return true
can_yield = (function(){
try {
return eval("!!Function('yield true;')().next()");
}
catch(e) {
return false;
}
})();
</script>
<script type="application/javascript">
if(!can_yield)
{
alert("Can't Yield!");
}
</script>
Tested in:
yield worksyield worksyield does not workyield does not work