When I run
/(a)/g.exec('a a a ').length
I get
2
but I thought it should return
3
because there are 3 as in the string, not 2!
Why is that?
I want to be able to search for all occurances of a string in RegEx and iterate over them.
FWIW: I'm using node.js
exec() is returning only the set of captures for the first match, not the set of matches as you expect. So what you're really seeing is $0 (the entire match, "a") and $1 (the first capture)--i.e. an array of length 2. exec() meanwhile is designed so that you can call it again to get the captures for the next match. From MDN:
If your regular expression uses the "g" flag, you can use the exec method multiple times to find successive matches in the same string. When you do so, the search starts at the substring of str specified by the regular expression's lastIndex property (test will also advance the lastIndex property).
You could use match instead:
'a a a'.match(/(a)/g).length // outputs: 3
Code:
alert('a a a'.match(/(a)/g).length);
Output:
3
You are only matching the first a. The reason the length is two is that it is finding the first match and the parenthesized group part of the first match. In your case they are the same.
Consider this example.
var a = /b(a)/g.exec('ba ba ba ');
alert(a);
It outputs ba, a. The array length is still 2, but it is more obvious what is going on. "ba" is the full match. a is the parenthesized first grouping match.
The MDN documentation supports this - that only the first match and contained groups are returned. To find all matches, you'd use match() as stated by mVChr.