[javascript] are conditional/contextual keywords a good idea?

[meraedit]

With the current grammar definition for javascript, some keywords cannot be used as identifier names, even though the browser supports them.
For instance
var form = 1;
is reported as a syntax error because 'from' is a keyword.

The es standard allows it: Keywords and Reserved Words
I noticed on the Readme page that the grammar defined in the g4 file does not exactly correspond to the ECMAScript standard,
but I think it would be nice to have those in the grammar:

conditionalKeyword : NonStrictLet | Static | Implements | Interface | Package | Private | Public | Protected | Async | Await | From | As | Yield ;
Attached the g4 file
JavaScriptParser.zip

Is there a better way to avoid getting syntax errors due to conditional keywords?

[KvanTTT]

You can use semantic predicates in the following way:

getter
    : {_input.LT(1).getText().equals("get")}? Identifier propertyName
    ;

But it's not a very good solution: it's target-specific and it looks cumbersome.

The feature for contextual keywords was suggested some time ago: Token value comparison operator. Unfortunately, unlikely it will be implemented in ANTLR 4.