Update javascript lexer

[Mesteery]

Partially resolves #1781.

[Anteru]

Merged, thanks! What's the rationale for removing .tsx as a Typescript alias?

[Mesteery]

What's the rationale for removing .tsx as a Typescript alias?

Because this lexer doesn't really support TSX.

[vlakoff]

Using a variable named from in plain JavaScript code, I noticed it was highlighted as a reserved word (though it isn't a reserved word actually).

I pinpointed the cause to the following code, introduced by this PR:

pygments/pygments/lexers/javascript.py

Lines 88 to 89 in 513f8fc

	# Match stuff like: constructor
	(r'\b(constructor|from|as)\b', Keyword.Reserved),

[Mesteery]

from is a reserved word. By the way, when you use 'strict mode', your code will fail if you use from as a variable name.
from is used with import like import something from 'package'.

[vlakoff]

My code is in strict mode, and it is currently using a variable named from, which doesn't fail.

I think that's because import, then subsequently from, is reserved only if the script if interpreted as a module. See the import documentation on MDN:

In order to use the import declaration in a source file, the file must be interpreted by the runtime as a module. In HTML, this is done by adding type="module" to the <script> tag. Modules are automatically interpreted in strict mode.

Though, I don't think Pygments can distinguish between the "regular" and "module" types…