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Luke Miles
Luke Miles

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Simple typescript data validation without libraries

#typescript #validation

Check that your function arguments have correct types at run-time!

import {validate} from './validate' const validGetUserArgs = Object.freeze({ authToken: '', pubkey: new PublicKey() atTime: new Date() }) type GetUserArgs = typeof validGetUserArgs function getUser(args: GetUserArgs) { validate(args, validGetUserArgs) checkToken(args.authToken) db.get({pubkey: args.pubkey, at: args.atTime}) }
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And here's one definition of that validate function:

function validate<T>(obj: T, valid: T) { for (const k in valid) if (!(k in obj)) throw Error(`missing key ${k}`) for (const k in obj) if (!(k in valid)) throw Error(`unknown key ${k}`) for (const k in obj) { const got = typeof obj[k] const wanted = typeof valid[k] if (got !== wanted) { throw Error(`argument ${k} had type ${got} instead of ${wanted}`) } } }
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Demo in typescript playground

Note this is limited. You'll have a headache with unions, optionals, nesting, non-class interfaces, etc.

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