Question

JavaScript1.7 error in GoogleChrome

Example:

var x, y;
try {
 [x, y] = ["1", "2"];
 document.write(x+": "+y);
} catch(e){
 console.log(e);
}

catch erro:
Invalid left-hand side in assignment JavaScript1.7

I need actually is to test if the browser supports javascript1.7

What I need is to actually test if the browser supports javascript1.7
But without using this kind of code:

jsversion = 1.7;

This code beyond invalid by the w3c, is also working with global variables,
which can be a very bad thing (can cause conflicts and other problems)

I tried using the following code (but error occurs in “strict”)

var i=0;
try{
    yield i;
} catch(ee) {
    document.write(ee);
}

So this is what I need to do, to test if the browser supports javascript1.7.

Thanks.

Answer 1

Try

var isESNext;
try {
  eval('(function () { var x, y; [x, y] = [1, 2]; })()');
  isESNext = true;
} catch (ex) {
  isESNext = false;
}

This uses eval to parse a bit of code which uses ES.next pattern decomposition but which is not valid EcmaScript 5. The rest of the code which declares and assigns isESNext is valid EcmaScript 3 code though so should run on all browsers.

The problem you’re running into is due to Chapter 16:

16 Errors

An early error is an error that can be detected and reported prior to the evaluation of any construct in the Program containing the error. An implementation must report early errors in a Program prior to the first evaluation of that Program.

…

An implementation must treat any instance of the following kinds of errors as an early error:

• Any syntax error.

But the code snippet above gets around the early error because

Early errors in eval code are reported at the time eval is called