JavaScript parentheses converts primitive type to object

Question

If numbers are primitive types, why I can do:

> (12345).toString()
"12345"

Is the parenthesis converting the primitive type to a Number ?

Answer 1

No, the parentheses are just letting the parser understand that the . is not a decimal point.

12345 .toString() will also work.

Primitive numbers implicitly converted to Numbers whenever you access their properties, but the objects are temporary and immediately lost. For example:

var foo = 5;

foo.bar = "something";

console.log(foo.bar); // undefined

Same goes for strings and booleans.

Answer 2

Actually, 1 .toString() works as well.

>>> typeof(Number(1)) === typeof(1)
true
>>> var a=1; a.toString()
"1"

It's the parser: 1.x expects x to be a digit.

>>> 1.toString()
SyntaxError: identifier starts immediately after numeric literal
[Break On This Error]   

You can find further explanation here

If primitives have no properties, why does "abc".length return a value?

Because JavaScript will readily coerce between primitives and objects. In this case the string value is coerced to a string object in order to access the property length. The string object is only used for a fraction of second after which it is sacrificed to the Gods of garbage collection – but in the spirit of the TV discovery shows, we will trap the elusive creature and preserve it for further analysis…