Why does 2..toString() work? [duplicate]

Question

Why does 2..toString() return 2 but 2.toString() throws this error?

Example:

console.log(2..toString()); // prints 2

// Firefox throws the error
// `SyntaxError: identifier starts immediately after numeric literal`
console.log(2.toString());

var x = 2;
console.log(x.toString()); // prints 2

// Firefox throws the error
//`TypeError: XML descendants internal method called on incompatible Number`
console.log(x..toString());

Answer 1

That's because 2. is parsed as 2.0, so 2..toString() is equivalent to 2.0.toString(), which is a valid expression.

On the other hand, 2.toString() is parsed as 2.0toString(), which is a syntax error.

Answer 2

2 is just a number, it doesn't have any methods to call.

2. can be coerced into a string, which is an object (i.e. '2.0'), hence can have the method.

Just 2.toString() will be parsed as 2.0tostring(), which of course doesn't make sense.

Looking at how the two are parsed:

vs

The tool to generate these is here by the way: http://jsparse.meteor.com/