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

Tue, 07 Apr 2026 00:00:00 +0000

I’ve been thinking about Alexis King’s Parse, don’t validate again. I do this quite regularly, actually, usually after staring at a TypeScript codebase that’s been quietly accumulating if (user.email) checks like barnacles. The post is from 2019, and the advice (or rather principle) is way older than that. And yet most TypeScript I read — including, embarrassingly, plenty I’ve written — still validates instead of parsing.

The pitch, if you haven’t read it (you should): a validator says “this thing is fine, please continue.” A parser says “give me a blob, and I’ll either give you back a more precise type or tell you why I can’t.” The difference sounds academic until you realize that validators throw away information the moment they finish running, while parsers preserve what they learned by encoding it in the type. Once you’ve parsed a string into an EmailAddress, the rest of your program never has to wonder again. Peace of mind and more mental capacity for the fun stuff.

Parsing on cekrem.github.io

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