How to prevent regular expression test toggling when using a variable?

Question

I just noticed the following strange behavior (both in browsers and nodejs:

> a = /^\/foo/g
/^\/foo/g
> a.test("/foo")
true
> a.test("/foo")
false
> a.test("/foo")
true
> a.test("/foo")
false
> a.test("/foo")
true

What kind of mad science we have here? How can I prevent this behavior?

I just want to have a regex variable that checks if a string matches the pattern globally.

---

Documentation pages don't seem to bring some light there... I'd really appreciate a link to documentation references.

Answer 1

Set the lastIndex of your regex to 0 after each test.

a = /^\/foo/g
a.test("/foo"); //true
a.test("/foo"); //false
a.test("/foo"); //true
a.lastIndex = 0; //reset the index to start the next match at beginning
a.test("/foo"); //true