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TS Functions

Functions in TypeScript allow you to define reusable blocks of code with strict type checking. They can have parameter types, return types, and optional or default parameters.

Key Topics

Function Syntax

TypeScript functions are defined with parameter types and return types for improved type safety.

function add(a: number, b: number): number {
    return a + b;
}

console.log(add(5, 10)); // 15

Output

15

Explanation: The add function takes two number parameters and returns a number. The return type is explicitly defined.

Optional Parameters

Parameters can be marked as optional using the ? operator. Optional parameters must appear after required parameters.

function greet(name: string, message?: string): string {
    return message ? `${message}, ${name}!` : `Hello, ${name}!`;
}

console.log(greet("Alice"));           // Hello, Alice!
console.log(greet("Bob", "Hi"));      // Hi, Bob!

Output

Hello, Alice!

Hi, Bob!

Explanation: The message parameter is optional. When not provided, the function defaults to a basic greeting.

Default Parameters

Default parameter values can be provided, ensuring the function works even if arguments are not explicitly passed.

function multiply(a: number, b: number = 1): number {
    return a * b;
}

console.log(multiply(5));     // 5
console.log(multiply(5, 3));  // 15

Output

5

15

Explanation: The b parameter has a default value of 1, which is used when the second argument is not provided.

Specifying Return Types

You can explicitly define the return type of a function to ensure it matches the expected type.

function isEven(num: number): boolean {
    return num % 2 === 0;
}

console.log(isEven(4));  // true
console.log(isEven(7));  // false

Output

true

false

Explanation: The isEven function returns a boolean based on whether the input num is even or odd.

Key Takeaways

  • Parameter Types: TypeScript enforces types for function parameters to catch errors at compile time.
  • Optional Parameters: Use ? to define parameters that may not always be provided.
  • Default Parameters: Provide default values to ensure functions work even when arguments are missing.
  • Return Types: Explicitly define return types for predictable and type-safe functions.
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