What is Type Annotations in TypeScript ? Last Updated : 21 Jan, 2025 Comments Improve Suggest changes Like Article Like Report TypeScript Type Annotations allow developers to explicitly define the types of variables, functions, and other elements in the program.They help catch mistakes early by ensuring the right data type is used.They make the code easier to understand and follow.Type Annotations help avoid errors and make the code more reliable. JavaScript const str: string = "GeeksforGeeks"; const num: number = 6; const arr: (number | string)[] = ["GFG", "TypeScript", 500, 20]; console.log(typeof str); console.log(typeof num); console.log(arr); str is assigned the type string, so it will only accept string values.num is a number type, ensuring it will only store numbers.arr is an array that can hold both number and string types.Output:string number ["GFG", "TypeScript", 500, 20]More Examples of Type AnnotationsFunction with Type Annotations JavaScript function greet(name: string): string { return `Hello, ${name}!`; } The greet function accepts a parameter name of type string and returns a string.This ensures that both the input and output are of the expected types, preventing type-related errors.Object with Type Annotations JavaScript const person: { name: string; age: number } = { name: "Alice", age: 30 }; The person object is explicitly typed to have a name of type string and an age of type number.This enforces the structure of the object, ensuring it adheres to the specified types.Array with Type Annotations JavaScript const numbers: number[] = [1, 2, 3, 4, 5]; The numbers array is annotated to contain only number elements.This prevents the inclusion of elements of other types, maintaining type safety. Class with Type Annotations JavaScript class Rectangle { width: number; height: number; constructor(width: number, height: number) { this.width = width; this.height = height; } area(): number { return this.width * this.height; } } The Rectangle class has width and height properties, both of type number.The area method returns a number, representing the area of the rectangle. Comment More infoAdvertise with us Next Article What is Type Annotations in TypeScript ? A abhish8rzd Follow Improve Article Tags : JavaScript Web Technologies TypeScript JavaScript-QnA WebTech-FAQs +1 More Similar Reads What is the Function type in TypeScript ? TypeScript is a JavaScript-based programming language with a typed syntax. It provides improved tools of any size. It adds extra syntax to JavaScript. This helps in facilitating a stronger interaction between you and your editor. It also helps in catching the mistakes well in advance. It uses type 3 min read What is Type Erasure in TypeScript? TypeScript is a very mighty superset of JavaScript, which adds static typing to the language and allows developers to catch errors early on as well as write more maintainable code. This being said a TypeScript type system erases type information at compile time (or during the compilation), a phenome 4 min read TypeScript Return Type Annotations TypeScript Return Type Annotations allow you to define the expected return type of a function, enhancing code clarity and type safety. By specifying the return type (functionName(): ReturnType), you ensure the function returns the correct type, catching mismatches and reducing potential errors durin 2 min read TypeScript Type Annotations on Variables TypeScript is a statically typed superset of JavaScript that brings the benefits of strong typing to the JavaScript ecosystem. One of its key features is the ability to add type annotations to variables, which helps developers catch type-related errors at compile time rather than runtime. In this ar 3 min read TypeScript Parameter Type Annotations TypeScript Parameter type annotations are used to specify the expected data types of function parameters. They provide a way to explicitly define the types of values that a function expects as arguments. Parameter type annotations are part of TypeScript's static typing system, and they help catch ty 2 min read Like