The "Restrict Possible Usernames" lesson is bugged

[anotherone.myemail]

Hello.

So I reached the “Restrict Possible Usernames” lesson in the “Regular Expressions” course

I wrote the right RegEx to pass the test (/^[a-z][a-z]+\d*$|^[a-z]+\d\d+$/gi) and even tested it on an another RegEx checker website with the test examples from the lesson

I put my code in the right place, but after I press the “Run the Tests” button to pass the test, I can’t pass it, and the console output writes me that my RegEx doesn’t match strings it should match

But as soon as I add the username.match(userCheck); line to the test - I’m able to pass it

Steps

So, I think, there is a bug here in the user solution checker somewhere

[liam.stojanovic]

Hey there,

I just re-tried doing this lesson. Our regex is almost the same, but what I did notice was your use of the //g flag. I only passed along the //i flag, and that seemed to work on my first try.

Not sure why the global flag goofs it; perhaps multiple words are passed along at once and matching all of them causes the boolean comparison to fail.

[ilenia]

it’s what happens with the test method using the g flag

Using test() on a regex with the “global” flag

When a regex has the global flag set, test() will advance the lastIndex of the regex. ( RegExp.prototype.exec() also advances the lastIndex property.)

Further calls to test(str) will resume searching str starting from lastIndex . The lastIndex property will continue to increase each time test() returns true .

RegExp.prototype.test() - JavaScript | MDN

[bbsmooth]

Bottom line, don’t use the global flag when using RegExp.test unless you understand the repercussions. I don’t think I can recall ever using the global flag with this method. RegExp.test returns a boolean, so it is just checking if the pattern matches, it isn’t returning any information about the matches, so having the global flag doesn’t really make sense. The global flag would be used when you anticipate more than one match in a string and want the information for each of those matches (see discussion of return value for String.match).

[lasjorg]

You can also reset lastIndex after the call to .test()

userCheck.lastIndex = 0;

---

This does seem to bite quite a few people. I seem to remember talking about resetting the index in the test code, or changing it from test to match.

[bbsmooth]

@lasjorg

This does seem to bite quite a few people.

It seems more of an issue that people don’t understand what the global flag does and are just adding it in there when it isn’t needed. If the variable username only contains one username then there is no reason to use the global flag regardless of the method used to test the regex.

[lasjorg]

Obviously, it’s a lack of knowledge about the global flag in the context of .test(). However, this has been a recurring issue and I know we did some fixes for other challenges.

Here is a related issue I was thinking about.

Regular Expressions: Restrict Possible Usernames - Should lastIndex be reset?

[anotherone.myemail]

That’s all what freeCodeCamp said about the global flag:

Link

Noting about the lastIndex of the global flag at the test() method.

And why does my solution work if I add the username.match(userCheck) line to the end?

[ilenia]

It may be that match reset the lastIndex of a regex, but I have not checked

that quote is also about using g flag with the match method, not with test

It’s impossible to put everything in the curriculum, there is a lot that is not mentioned

String.prototype.match() - JavaScript | MDN

[lasjorg]

I think it’s just because Match is a string method and lastIndex is a property on a RegExp instance.

---

The issue with this challenge isn’t really with the global flag. The problem is with the seed code advancing lastIndex. If you comment out (or remove) all the code except for the regex, it will pass the tests.

// let username = "JackOfAllTrades";
let userCheck = /^[a-z][a-z]+\d*$|^[a-z]+\d\d+$/gi; // Change this line
// let result = userCheck.test(username);