using the proper algorithm you shouldn't run into that issue. But that's a valid concern. I'll add it to the description.

I agree with this. My code works fine until the last random number where it takes too long to run. As a beginner, I have no idea how to fix this so I think it is more appropriate as a lower kyu level if that last part is to be left in.

There is no "output" for this kata. A given string is tested against the regex (or vis versa, depending on how you look at it). So if you match anything, the test will be successful.

So for example:

var Mod4 = /\[\+05620\]/g;
Mod4.test("[+05620]") // will return `true`, meaning the given string has a valid mod4 within it