Why does 00.0 cause a syntax error?

Question

This is weird. This is what happens at the JavaScript console in Chrome (version 42.0.2311.135, 64-bit).

> 0
< 0
         


        

Answer 1

The expressions 0.0 and 00.0 are parsed differently.

• 0.0 is parsed as a numeric literal ¹
• 00.0 is parsed as:
  • 00 – octal numeric literal ²
  • . – property accessor
  • 0 – identifier name

Your code throws syntax error because 0 is not a valid JavaScript identifier. The following example works since toString is a valid identifier:

00.toString

¹ Section 7.8.3 – Leading 0 can be followed by decimal separator or ExponentPart
² Section B.1.1 – Leading 0 can be followed by OctalDigits