Javascript weird dot operator syntax [duplicate]

问题:

This question already has an answer here:

• What are the rules for invoking functions on number literals in JS? [duplicate] 1 answer

In Chrome console, also test in edge and firefox

5.toFixed(2);

get

Uncaught SyntaxError: Invalid or unexpected token

in chrome.

SyntaxError: identifier starts immediately after numeric literal

in firefox.

Expected ';'

in edge.

But code below

5.1.toFixed(2);
(5).toFixed(2);

is ok in all three browsers above.

回答1:

This is because of the JavaScript parser assuming the dot in for example 5.toFixed(2) belongs the number literal. (As in 5., which is a valid number literal.) This is because JavaScript parses (at least number literals) greedily.

If you do (5).toFixed(2) however, it is clear to the parser what you want (the dot clearly is not a part of the number literal).

Same with 5.1.toFixed(2). The second dot clearly cannot belong to the number literal, so the parser has a better time with it.