Remove everything after a certain character

Handling variety of strings

Strings come in all forms; what if the delimiter doesn't exist? Be prepped with indexOf():

const url = (s) => s.includes('?') ? s.substring(0, s.indexOf('?')) : s;
console.log(url("http://example.com?param=value")); // "http://example.com"
console.log(url("http://example.com")); // "http://example.com"
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Well aren't we fancy? Handling URLs even without exceptions!

For the regex buffs, here's a swift solution using replace():

const str = "http://example.com?param=value";
const base = str.replace(/[\?#].*$/, '');
console.log(base); // "http://example.com"
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Ah regex, the Sith language of JavaScript. Here, '?' or '#' have met their match!

Going deeper: Advanced techniques and pitfalls

Navigating URL intricacies

We're not forgetting URL hashes, fragments, and pesky multi-parameters:

const fullURL = "http://example.com?param=value#anchor";
const base = fullURL.split(/[?#]/)[0];
console.log(base); // "http://example.com"
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Take that multiple delimiters! Tested your regex chops yet?

Keeping the path, ditching the query

Reckon keeping the URL path while purging those annoying query strings:

const pathWithQuery = "http://example.com/path?query=123";
const pathOnly = pathWithQuery.substring(0, pathWithQuery.indexOf('?'));
console.log(pathOnly); // "http://example.com/path"
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Now we're talkin', the path is preserved! The ? does not have the last say.

Replace and the unknown

Not sure what's trailing your delimiter? Use $' in replace() to insert what comes after:

const replaceQuery = (url) => url.replace(/\?.*$/, '');
console.log(replaceQuery("http://example.com/path?query=123")); // "http://example.com/path"
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Replaced what? Doesn't matter, it's gone!

Err on the side of caution: Testing assumptions

Ensure accuracy by testing with several string scenarios:

1. Strings with multiple delimiters: "keep|keep|discard".
2. Without the delimiter: "keep this all".
3. Extremes like empty strings or trailing delimiter: "", "keep this|".

Ain't no string gonna catch you off-guard, you've got 'em all covered.

Avoiding rookie mistakes

Assuming delimiter presence is given

Presence of delimiter matters, as its absence can crash your function — that's pure mayhem!

Not expecting malformed input

Assumptions about input are dangerous. Run your function with aberrant/edge case data to make it foolproof.

Over-engineering

Pick the simplest effective solution. You're programming, not building Frankenstein's monster.