How to Define Functions with Specific Argument and Return Types in TypeScript

TypeScript allows you to define functions with explicit argument and return types. This ensures type safety and helps catch errors at compile time.

Defining Argument and Return Types

You can annotate each parameter with its type and the return type after the function's parentheses.

Syntax:

function functionName(param1: Type1, param2: Type2): ReturnType {
  // function body
}

Example 1: Simple Addition

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

• a and b are both required to be numbers.
• The function returns a number.

Example 2: String Formatter

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

• The parameter name must be a string.
• The function returns a string.

Using Arrow Functions

You can also define typed arguments and return types in arrow functions.

const multiply = (x: number, y: number): number => x * y;

Benefits

• Prevents passing or returning incorrect types
• Improves code documentation and readability

Tip

If a function doesn’t return anything, use void as the return type:

function logMessage(msg: string): void {
  console.log(msg);
}