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Practical tutorials for the work we actually do. Pick one, read it in order, and apply it.

Any category Programming12 Python 2 JavaScript 5 TypeScript 5
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TypeScript APIs and Integrations Clear filters 5 results
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Discriminated Unions for success and error Responses

Replace a data-or-error object with a union tagged by success, then add a generic Outcome and an unwrap helper. After this, the compiler knows which property exists in each case.

4 min read
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Type JSON from fetch Without as MyType Everywhere

Replace scattered casts with one assertion function and one typed fetch helper. After this, a 404 or a changed payload fails with a clear message instead of carrying a wrong type.

3 min read
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unknown First, Then Narrow: Parse an API Payload

Receive a nested payload as unknown and narrow it with two small helpers until every property is checked. After this, you can write a parser that rejects wrong data and returns a real type.

3 min read
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Augment Express Request Without Fighting the Compiler

Add a user property to the Express request type with a module augmentation in one declaration file. After this, middleware and handlers agree on the type and you avoid the mistake that floods node_modules with errors.

5 min read
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Template Literal Types for /users/:id Routes

Turn a route pattern into a type that finds the parameter names and checks the paths you pass. After this, a typo in a route or a missing parameter is a compile error.

5 min read