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Browser support for possessive quantifiers

For the second regular expression,

re2

, the following takes place behind the scenes:

re2.test(“a”); //false - no match

re2.test(“ab”); //false - no match

re2.test(“abb”); //false - no match

re2.test(“abbb”); //true – match!

//store this result and start with next letter

re2.test(“a”); //false - no match

re2.test(“aa”); //false - no match

re2.test(“aab”); //false - no match

re2.test(“aabb”); //true – match!

re2.test(“aabbb”); //true – match!

//store this result and start with next letter

re2.test(“a”); //false - no match

re2.test(“aa”); //false - no match

re2.test(“aaa”); //false - no match

re2.test(“aaab”); //true – match!

re2.test(“aaabb”); //false - no match

re2.test(“aaabbb”); //true – match!

//store this result and start with next letter

re2.test(“1”); //false - no match

re2.test(“12”); //false - no match

re2.test(“123”); //false - no match

re2.test(“1234”); //false - no match

//done

Since

re2

contains a reluctant quantifier, it returns

“abbb”

“aabbb”

, and

“aaabbb”

, just as you’d

expect.

The final regular expression,

re3

, actually has no result because it’s possessive. Here’s what it does

behind the scenes:

re3.test(“abbbaabbbaaabbb1234”); //false – no match

Because possessive quantifiers only do one test, if that test fails, you get no result. In this case, the

“1234”

at the end of the string causes the expression not to match. If the string were simply

“abb-

baabbbaaabbb”

, then

re3

would have returned the same result as

re1

Browser support for possessive quantifiers leaves much to be desired. Internet

Explorer and Opera don’t support possessive quantifiers and throw an error when

you try to use one. Mozilla won’t throw an error, but it treats possessive quantifiers

as greedy.

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