Start using TypeScript
Types do not change runtime behavior
Understand that annotations are erased and cannot validate a network response, form value, or JSON file while the program runs.
This assertion tells TypeScript to trust you:
const user = (await response.json()) as UserIt does not inspect the response body. The server can still return null, an error object, or a user with missing fields.
Types also do not convert values:
const port = process.env.PORT as unknown as numberAt runtime, an environment variable is still a string. The assertion changes only what the checker believes.
Treat values from JSON, forms, storage, environment variables, and network calls as uncertain. Check them at the boundary before using a more specific type.
For a user, that means verifying the value is an object and checking the fields your program needs. A schema library can help, but ordinary JavaScript checks work too.
Exercise: log typeof process.env.PORT at runtime. Compare that result with what an unsafe assertion can make TypeScript claim.
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