alt Hacker NewsProtip: never even mention undefined in your codebase. Erase it from your vernacular. If you ever need to pass or return nothing, you use null.
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You can't get rid of undefined. You can't ban null either. They're both used in the core language all over the place:
undefined camp:
- out of bounds array index access [1,2,3][42]
- non existent object key access {}.foo
- array.find(...) no result
- ...
null camp:
- document.querySelector(...) no result
- regex.match(...) no result
- ...
If you're a type purist then undefined looks nicer... It'd be like being upset at booleans because things get coerced to them or some 'ish.
No: it's the type that has one inhabitant—it's not that type's fault that it appears as a default argument or var or was left out of JSON... So long as typeof null === "object", null is the absurd one
null is of type 'object' though, while undefined is undefined - way better to have a separate type.
I do it this way, but this led to people asking me in reviews why I use NULL^^
My explanation was that it signals intent to me, and is different from some property not being part of the expected object shape or not having been initialized because of some accident or logic failure.
Since then, I've sticked to it, and am "allowed" to use NULL ^^
It can lead to some annoying checks in TS for primitively-typed properties, so for these, I still allow explicit usage of undefined when it's simpler given the surrounding code.
But I agree with you in principle. Using "undefined" as a "second nullish value" and explicitly checking for it is a programming error.
When there's object/areay vs null/undefined, thankfully, the truthiness narrowing often allows me to interface with code relying on "undefined" without explicitly handling this "value" in my own parts of the code base :)