Why toString() can be called on arguments but not directly

Question

So I have this:

5.toString()

I get this error:

console.log(5.toString());
            ^^

SyntaxError: Invalid or unexpected token
    at new Script (vm.js:79:7)
    at createScript (vm.js:251:10)
    at Object.runInThisContext (vm.js:303:10)
    at Module._compile (internal/modules/cjs/loader.js:657:28)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)
    at Module.load (internal/modules/cjs/loader.js:599:32)

However, if I pass 5 using an intermediary function, it seems to cause no problems:

const foo = function(v){
  console.log(v.toString());
};


foo(5);   // no problem now

does anyone know why that runs without an error? I would think it would cause an exception. Maybe it's just a "compile-time" exception, not a runtime exception.

Possible duplicate of [Why can't I access a property of an integer with a single dot?](https://stackoverflow.com/questions/9380077/why-cant-i-access-a-property-of-an-integer-with-a-single-dot) — CertainPerformance, Sep 20 '18 at 23:29
The `SyntaxError` tells you that it's a compile-time error, not a runtime error. — CertainPerformance, Sep 20 '18 at 23:30

Lev Kuznetsov · Accepted Answer · 2018-09-20T23:32:55.433

0

Put it in parens like this:

(5).toString()

You can't use it the other way because the lexer is thinking you're typing out a decimal number

edited Sep 20 '18 at 23:32

answered Sep 20 '18 at 23:30

Lev Kuznetsov

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Can you provide an explanation? – Adam Sep 20 '18 at 23:31
Sounds like auto-boxing (what happens in Java too)...using parens makes it an object instead of a primitive. – Sep 20 '18 at 23:35
I think `5..toString()` (with two dots) also does the same thing – Sep 20 '18 at 23:36

Why toString() can be called on arguments but not directly

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