correctly creates the binary string "10011000", but
throws an exception
"SyntaxError: identifier starts immediately after numeric literal"
Why? The latter syntax actually sounds more correct while the former looks very odd!
. 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.
@pedants and downvoters
. 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.
The lexer (aka "tokenizer") when reading a new token, and upon first finding a digit, will keep consuming characters (i.e. digits or one dot) until it sees a character that is not part of a legal number.
<152.> is a legal token (the trailing 0 isn't required) but
<152..> isn't, so your first example reduces to this series of tokens:
<152.> <.> <toString> <(> <2> <)>
which is the legal (and expected) sequence, whereas the second looks like
<152.> <toString> <(> <2> <)>
which is illegal - there's no period token separating the Number from the
10. is a
float number an you can use toString on
parseFloat("10").toString() // "10"
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