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I noted that we don't have token specific fixtures, should we add those?
Moreover#13417 also mentions thatvalue for the most of the tokens isundefined. We may do something like this in the Token constructor:

constructor(state:State){this.type=state.type;if(state.value!==undefined){this.value=state.value;}this.start=state.start;this.end=state.end;this.loc=newSourceLocation(state.startLoc,state.endLoc);}

but no tests are throwing, since they are not writingvalue in the output ifundefined.

Thanks for the quick fix, have you checked|} token as well?

I noted that we don't have token specific fixtures, should we add those?

@fedeci You can add a newbabel-parser/test/tokens.js file with normal describe-it-expect Jest tests, or a new subfolder oftest/fixtures.

We need similar fix for[| and{|.

That token constructor code is super slow :) Why there is a need for anew SourceLocation. Can't this be a plain object?
And regarding the "missing" value. All object should keep the same shape to avoid hidden classes issue and perf regression in V8.

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@JLHwung No plans to fix the performance issues?

@KFlash I am aware of the performance issue here, but fixing the performance falls out of the scope of this PR and thus should be addressed in another PR.