Q44. How should environment variables be typed?
Environment variables are runtime strings and may be missing, even when a declaration file claims otherwise. Define compile-time types for known names if helpful, but parse and validate values at startup. Numbers, booleans, URLs, and secrets should not be blindly trusted as already-correct typed values.
A declaration such as DB_PORT: string does not turn the environment value into a number or guarantee it exists.
Note
Interview approach: define the concept, explain why it matters, then mention one trade-off or limitation.
TypeScript concept
// Illustrative TypeScript contract
type Identifier = string;
const id: Identifier = "item-1";💡 The example demonstrates the compile-time contract discussed in this question.
Key Takeaways
- Explain the concept in your own words.
- Know the practical trade-off and its limits.
- Use a small example to demonstrate the idea.
Knowledge Check
What is needed beyond a TypeScript declaration for `PORT`?