Can someone explain in detail what is going on here? Specifically the double dot notation.
(3.14).toFixed(); // "3"
3.14.toFixed(); // "3"
(3).toFixed(); // "3"
3.toFixed(); // SyntaxError: Unexpected token ILLEGAL
3..toFixed(); // "3"
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This question is similar to: Why is it only valid syntax to perform property access on a numeric literal when a space precedes the dot (`.`) operator?. If you believe it’s different, please edit the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem.dumbass– dumbass2024-11-12 12:53:18 +00:00Commented Nov 12, 2024 at 12:53
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2 Answers
According to ECMA Script 5.1 Specifications, grammar for decimal literals are defined like this
DecimalLiteral :: DecimalIntegerLiteral . [DecimalDigits] [ExponentPart] . DecimalDigits [ExponentPart] DecimalIntegerLiteral [ExponentPart]
Note: The square brackets are just to indicate that the parts are optional.
So, when you say
3.toFixed()
After consuming 3., the parser thinks that the current token is a part of a Decimal Literal, but it can only be followed by DecimalDigits or ExponentPart. But it finds t, which is not valid, that is why it fails with SyntaxError.
when you do
3..toFixed()
After consuming 3., it sees . which is called property accessor operator. So, it omits the optional DecimalDigits and ExponentPart and constructs a Floating point object and proceeds to invoke toFixed() method.
One way to overcome this is to leave a space after the number, like this
3 .toFixed()
Comments
3. is a number, so the . is the decimal point and doesn't start a property.
3..something is a number followed by a property.
