Parameters type in Typescript

Introduction

Parameters type helps you tell the computer what kind of information a function expects. This makes your code safer and easier to understand.

When you want to make sure a function only gets numbers as input.

When you want to describe that a function needs a string and a number.

When you want to avoid mistakes by checking inputs before running code.

When you want to help others understand what kind of data your function needs.

Syntax

Typescript

function functionName(parameterName: parameterType) {
  // function body
}

The parameterName is the name you give to the input inside the function.

The parameterType tells what kind of data the function expects, like string, number, or boolean.

Examples

This function expects a string called name and prints a greeting.

Typescript

function greet(name: string) {
  console.log(`Hello, ${name}!`);
}

This function expects two number parameters and returns their sum.

Typescript

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

This function takes a number and returns a boolean telling if the age is 18 or more.

Typescript

function isAdult(age: number): boolean {
  return age >= 18;
}

Sample Program

This program defines a function that multiplies two numbers and prints the result.

Typescript

function multiply(x: number, y: number): number {
  return x * y;
}

const result = multiply(4, 5);
console.log(`4 times 5 is ${result}`);

Important Notes

If you pass the wrong type, TypeScript will show an error before running the code.

You can make parameters optional by adding a question mark, like name?: string.

Using parameter types helps catch mistakes early and makes your code easier to read.

Summary

Parameter types tell what kind of data a function expects.

This helps prevent errors and makes code clearer.

Use simple types like string, number, and boolean for parameters.