hasBasename bugfix

[hmate9]

Previously it didn't work when prefix had special regex characters (eg $)

[mjackson]

I'm uncomfortable merging this because I think that using a regex in the underlying code is probably too complex for our needs. All we really need to do is make a string comparison that asserts the next char is one of the URL-delimiting characters (i.e. /, ?, #) or the end of the string.

Would you be open to doing a more extensive refactoring here?

[Parakleta]

I use the following successfully:

export const hasBasename = (path, prefix) =>
    path.startsWith(prefix) && "/?#".indexOf(path.charAt(prefix.length)) !== -1;

This obviously works in the delimited case, but in the end-of-string case it also works because the charAt function returns the empty string if the length is past the end, and indexOf always returns 0 when called with the empty string as an argument.

[hmate9]

@Parakleta I added your change to the PR, just also converting path and prefix to lowercase to make sure the matching is case insensitive.

[hmate9]

@mjackson could you please comment on this PR. Is it ready to be merged?

[mjackson]

Is there a particular reason you're using lastIndexOf instead of indexOf here?

[mjackson]

Thanks for working on this, @hmate9. Looks great. Just curious about the usage of lastIndexOf instead of indexOf.

[Parakleta]

lastIndexOf with a fromIndex of 0 is functionally equivalent to startsWith in this case but is available everywhere (lastIndexOf is ES1, startsWith is ES6). Alternatively you could use something like path.substr(0, prefix.length) === prefix which is ES3.

[Parakleta]

No, don’t do that, performance is a dog. Leave it as it was.

ETA: to expand, indexOf will check every position even though you’re only interested in the first, wasting time. lastIndexOf only checks the first position because it’s the last it can check and you told it to start there. The substr example I gave previously is less confusing, but is wasteful because it creates a new string object to check against (although maybe if JS has interning and is smart this might be free).

IMO, If ES6 is OK (or polyfilled or transpiled) then use startsWith, otherwise use substr if performance is less important than clarity, otherwise use lastIndexOf, maybe with a comment explaining what it does.

[hmate9]

@Parakleta Are you sure about that? According to the docs:

The indexOf() method returns the index within the calling String object of the first occurrence of the specified value.

It wouldn't make sense to look for more than one match if you have already found one.

[Parakleta]

You’re assuming you find a match...

Put this way, the lastIndexOf is O(min(m,n)) for match or no. The indexOf version is O(m) on a match, and O(m*n) => O(n^2) on no match. Quadratic is bad.

[hmate9]

@Parakleta cool, makes sense. Thank you. What do you think @mjackson ? Should I change it back to lastIndexOf?

[hmate9]

@mjackson could we get an update on this please?

[hmate9]

ping @mjackson

This is ready to be merged and is pretty useful fix

[avrahams1]

Is this going to be merged soon?

[bjarkehs]

Any news on this? I just ran into this issue myself.

[ajhyndman]

I'm running into this too. I also realized that there are 4 other PRs that have been opened since, attempting to fix the same bug.

#608
#607
#604
#566

It's been six months, so maybe another ping for @mjackson is in order.

[marconi]

we just ran into this as well LGTM! 👍

[mjackson]

Thanks for the PR, @hmate9, and sorry for sitting on it for so long. I just merged this manually. It will be released in 4.10 and will be present in the 5.0 release as well.

[Parakleta]

I think you should be using one of substr, startsWith, or lastIndexOf as discussed in #544 (review) in place of the indexOf(prefix.toLowerCase()).