Why does 10..toString() work, but 10.toString() does not? [duplicate]

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A . after a number might seem ambiguous. Is it a decimal or an object member operator?

However, the interpreter decides that it’s a decimal, so you’re missing the member operator.

It sees it as this: 

(10.)toString();  // invalid syntax

When you include the second ., you have a decimal followed by the member operator.

(10.).toString();

@pedants and downvoters

The . character presents an ambiguity. It can be understood to be the member operator, or a decimal, depending on its placement. If there was no ambiguity, there would be no question to ask.

The specification’s interpretation of the . character in that particular position is that it will be a decimal. This is defined by the numeric literal syntax of ECMAScript.

Just because the specification resolves the ambiguity for the JS interpreter, doesn’t mean that the ambiguity of the . character doesn’t exist at all.

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