I felt like the formatting of the grammar was a little difficult to read, namely the function/method calls, so I formatted them and took out the arguments lists into a shared fragment. I also formatted the rest of the file using Langium's default grammar formatter.

The new formatting is also closer to how JavaScript/TypeScript people format code.

Sidenote, the formatter wants to un-indent the comment, which was out of my controls:

    ({infer MemberCall.previous=current} 
        "." element=[NamedElement:ID] ( FunctionCallArguments )? 
    // Chained function call
        | ( FunctionCallArguments )
    )*;

The formatter would need a tweak so that it will instead do this:

    ({infer MemberCall.previous=current} 
        "." element=[NamedElement:ID] ( FunctionCallArguments )? 
        // Chained function call
        | ( FunctionCallArguments )
    )*;