856448 - Regular Expressions documentation: syntax of repetitions

Status: RESOLVED FIXED

(Developer Documentation Graveyard :: JavaScript, defect, P1)

Description

[Ken Harris]

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_4) AppleWebKit/536.25 (KHTML, like Gecko) Version/6.0 Safari/536.25

Steps to reproduce:

In the MDN "Regular Expressions" documentation <https://developer.mozilla.org/en-US/docs/JavaScript/Guide/Regular_Expressions#special-quantifier-range>, it says:

    "{n,m}    Where n and m are positive integers. Matches at least n and at most m occurrences of the preceding character. When either n or m is zero, it can be omitted."

The last sentence of this looks wrong to me.  I've not been able to reproduce this behavior in Firefox, or in Safari, or find it in the ECMAscript spec.



Actual results:

Empirically, in both Firefox and Safari, it seems you are able to omit m, only, when it is infinite (not zero).  Omitting n causes the RegExp object to treat the "{" character as a literal:

/^x{,3}$/.exec("x")
=> null

/^x{,3}$/.exec("x{,3}")
=> ["x{,3}"]

Specifically, whenever a "{" is followed by a non-digit character, it appears to be treated as a literal "{" character.


Expected results:

The ECMAscript spec RegExp grammar also makes no mention of being able to omit the first number in an {n,m} repetition: <http://www.ecma-international.org/ecma-262/5.1/#sec-15.10.1>.

I believe the documentation is incorrect.  Instead of the sentence:

    "When either n or m is zero, it can be omitted."

it should say something like:

    "When m is infinite, it can be omitted; n is always required."

Comment 1

[Eric Shepherd [:sheppy]]

Oops, moved the wrong bug. Putting it back.

Comment 2

[Tooru Fujisawa [:arai]]

Fixed the page:
  https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions