For static type checking code is analyzed by IDE at the time of writing the code. it is a **development tool** and compiles into plain JavaScript. It does not change the runtime behaviour of JavaScript code. Once TypeScript’s compiler is done with checking your code, it **erases the types** to produce the resulting “compiled” code. This means that once your code is compiled, the resulting plain JS code has no type information.

What is TypeScript?

Difficulty: 5/10

static typing, type inference, transpilation

TypeScript is a superset of JavaScript that adds static types to JavaScript.

1
For static type checking code is analyzed by IDE at the time of writing the code.
2
it is a development tool and compiles into plain JavaScript.
3
It does not change the runtime behaviour of JavaScript code.
4
Once TypeScript’s compiler is done with checking your code, it erases the types to produce the resulting “compiled” code.
5
This means that once your code is compiled, the resulting plain JS code has no type information.

Scenario Questions

0-2 years experience

1We have a small Node script written in JavaScript. How would you add TypeScript to it and what steps are required to run it?
2If you declare a variable as `let count: number` and later assign a string to it, what will happen at compile time and at runtime?
3Write an interface for a `User` object with `id`, `name`, and optional `email`, then use it in a function that logs the user's name.

Follow-up Questions

Can you show a quick code snippet that illustrates the benefit?
What are the trade‑offs of using strict mode?
How does the TypeScript compiler fit into a CI pipeline?