TypeScript promised the moon: static types in JavaScript’s wild west. Devs bought in hard—adoption hit 80% in state-of-the-union surveys by 2023, per Stack Overflow. But runtime? Still JS chaos. Enter ‘Parse, Don’t Validate,’ a battle cry from Cekrem’s blog that’s ruffling feathers in r/programming.
What everyone expected was more validators—Zod, Yup, that parade of schema enforcers ballooning npm downloads. This flips the script. Parse inputs directly into typed structures. No ‘if invalid, throw.’ Just safe data or failure. Changes everything for API handlers, form processors.
Look.
TypeScript fights it tooth and nail. Structural typing shines at compile-time, but runtime’s duck-typed JS laughs. You can’t ‘newtype’ without hacks. Cekrem nails it: the language “doesn’t want you to.”
Why Does TypeScript Make Parsing So Damn Hard?
It’s baked-in. TS types erase at runtime—poof, gone. So you’re left with typeof checks, brittle as glass. Market dynamics? Validator libs dominate: Zod alone pulls 10M weekly downloads. Parsing tools? Crickets.
But here’s the data: error rates in prod drop 20-30% with parse-first, per internal Stripe metrics leaked in talks. They parse JSON to branded types. No validation step. Fail fast on malformed input.
Cekrem’s post cuts through:
“Validation is a leaky abstraction. It checks, then reconstructs—prone to inconsistencies. Parsing builds the value directly, ensuring totality.”
Spot on. Validators lie: pass a string, get a ‘number’ that’s still a string underneath. Parse? You get Number or bust.
And.
TypeScript’s discriminated unions beg for this. { kind: ‘user’ | ‘admin’ }—parse narrows it perfectly. No extra runtime tax.
Is ‘Parse, Don’t Validate’ Just Hype for TypeScript Shops?
Nah. Historical parallel: Ruby on Rails ditched XML parsing for JSON-like simplicity early 2010s. Result? MVC explosion. TS could mirror that—faster iteration, fewer footguns.
My bold prediction: by 2025, TSX will ship native parse helpers. NPM’s parse-ts repo already forks wildly post-Cekrem. But corporate spin? MSFT’s TS team pushes io-ts forks, not pure parse. Smells like hedging.
Short para. Devs hate it now—surveys show 60% stick to Zod for ‘safety.’ Wrong. Zod’s 2MB bundles bloat Vercel deploys.
Deeper dive. Take a POST /users endpoint. Traditional:
function validateUser(input: unknown) {
if (!isObject(input)) throw new Error();
const name = input.name as string; // lie
// 20 more lines
return { name };
}
Parse way:
function parseUser(input: unknown): User | ParseError {
// build via pattern matching
return match(input, {
object: ({ name }) => ({ kind: 'user', name }),
else: () => ({ error: 'bad shape' }),
});
}
Leaner. Total. Scales to megacorps—see Effect-TS lib gaining 500k downloads.
Critique time. Cekrem glosses perf hits—parsing reflects unions, costly for deep nests. My insight: pair with lazy parsing. Eval only on access. TS 5.4’s satisfies() hints at it.
But so what? JS market’s $100B+ ecosystem. TS owns 70%. This shifts validation fatigue to parse purity.
Wander a sec. Remember Flow? Died ‘cause runtime ignored it. TS won’t—parse glues compile to runtime.
Can This Scale Beyond Toy APIs in TypeScript?
Data says yes. Remix.run mandates parse-first; their error rates halved. Cloudflare Workers? Parsing everywhere, no Zod.
Skeptical take. TS monorepos (Yarn PnP hell) choke on parse lib bloat. Fix? Stdlib it.
One sentence: Revolution brewing.
Dense block now. Enterprises balk—compliance needs audit trails. Validators log rejections easy; parsers fail silently (if you botch). Fix with ParseError types—telemetry gold. Gartner predicts 40% runtime type adoption by 2026; parse leads. Competitors? Rust’s serde parses natively—TS envies that.
Em-dash aside—TS devs, you’re validating shadows. Parse the light.
Parenthetical: (Zod’s creator admits it; check his tweets.)
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Frequently Asked Questions
What is ‘parse, don’t validate’ in TypeScript?
It’s transforming unknown inputs directly into typed values, skipping separate checks—failures bubble as type errors.
How do you implement parse don’t validate in TypeScript?
Use libs like @effect/schema or safe-parse patterns with branded types; match on shapes for discriminated unions.
Does parse don’t validate replace Zod in TypeScript?
Not fully—hybrids work—but pure parse cuts bundle size 50% and boosts reliability for APIs.
