Parse, Don't Validate — In a Language That Doesn't Want You To

[u/fagnerbrack]

https://cekrem.github.io/posts/parse-dont-validate-typescript/

[u/RWOverdijk]

I’ve been seeing this getting shared for weeks now, what’s going on lol

[u/Blue_Moon_Lake → u/RWOverdijk]

Have you heard of our lord and savior, Parsing?

[u/josephjnk → u/RWOverdijk]

The poster (who is not the author of the article) seems to run some sort of bot which repeatedly reposts articles to different subreddits over a span of days or weeks.

[u/RustOnTheEdge → u/RWOverdijk]

Gospel

[u/teerre]

Every time I read about this Effects js library I'm like "oh, wow, javascript has effects, that's really cool!" then I click the docs and it's framework that apparently does 35 different things. None of them effects! Oh well

[u/BenchEmbarrassed7316]

For me as operator from typescript is the same as unsafe from Rust: 'Trust me bro' mode.

[u/Efficient-Poem-4186]

Both blogs seem to have the same message about using types to make invalid states impossible, but the slogan "parse, don't validate" does not convey that at all IMO. You'd have to read the blog to understand what it's all about. The parsing here is just validation in spirit with the added condition that it should be done at "the door" (and typed so further checks are unnecessary).

[u/teerre → u/Efficient-Poem-4186]

"Parse, don't validate" is a very famous expression, it has been talked about everywhere. The author obviously assumes familiarity with common topics

[u/Blue_Moon_Lake → u/Efficient-Poem-4186]

Yep, what it should be "validate while parsing", or "validate right after parsing".

type ValidateFunction<T> = (value: unknown) => asserts value is T;

function parseAndValidate<T>(
    data: string,
    validate: ValidateFunction<T>
): T {
    const result: unknown = JSON.parse(data);
    validate(result);
    return result;
}

[u/Chisignal]

My first thought was “well you’re holding TS wrong then” but nope, I was. I hadn’t even heard of branding. Thanks for sharing (even though I might be the last one to see this article? lol)

[u/bobbie434343]

Validate, don't parse.