Parameter type annotations in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a parameter type annotation in TypeScript?

A parameter type annotation specifies the expected type of a function's parameter, helping catch errors and improve code clarity.

beginner

How do you add a type annotation to a function parameter in TypeScript?

You add a colon (:) after the parameter name followed by the type. Example: <code>function greet(name: string) {}</code>

beginner

What happens if you pass a wrong type to a function parameter with a type annotation?

TypeScript will show a compile-time error, preventing the code from running until the type mismatch is fixed.

beginner

Can you annotate multiple parameters with different types in a function?

Yes, each parameter can have its own type annotation. Example: <code>function add(a: number, b: number): number { return a + b; }</code>

beginner

Why are parameter type annotations helpful for beginners?

They guide you to use the right types, catch mistakes early, and make your code easier to understand and maintain.

How do you write a parameter type annotation for a string parameter named 'text'?

A text: string

B string text

C text = string

D text -> string

In TypeScript, the correct syntax is parameterName: type, so text: string is correct.

What error will TypeScript show if you call greet(123) when function greet(name: string) is defined?

A No error, 123 is accepted

B Runtime error

C Syntax error

D Type 'number' is not assignable to type 'string'

TypeScript checks types at compile time and will report that a number cannot be used where a string is expected.

Can you omit parameter type annotations in TypeScript?

A Yes, but then the parameter type is 'any' by default

B No, they are mandatory

C Yes, but only for numbers

D No, it causes a syntax error

If you omit the type, TypeScript treats the parameter as 'any', which disables type checking for that parameter.

Which of these is a valid function with two parameters annotated with types?

A function sum(number a, number b) {}

B function sum(a, b) {}

C function sum(a: number, b: number) {}

D function sum(a - number, b - number) {}

Option C uses correct TypeScript syntax for parameter type annotations.

What is the main benefit of parameter type annotations?

A They make code run faster

B They help catch type errors before running the code

C They reduce file size

D They allow dynamic typing

Parameter type annotations help catch mistakes early by checking types during development.

Explain how to add type annotations to function parameters in TypeScript and why it is useful.

Think about how you tell TypeScript what kind of data a function expects.

Describe what happens if you pass a wrong type to a function parameter that has a type annotation.

Consider how TypeScript helps avoid bugs before running the program.