TypeScript Optional Parameters in Callbacks: Main Insights

TypeScript is a popular programming language used to build powerful and scalable applications. In TypeScript , callback parameters are optional, which means they may or may not be provided when calling the callback.

Key Details About TypeScript Optional Parameters in Callbacks

Syntax:

type MyCallback = (param1: string, param2?: number) => void; function processCallback(callback: MyCallback, param1: string, param2?: number) { callback(param1, param2); }

In there:

• MyCallback is a type that represents a callback function that requires param1 (string) and a param2 (number).
• processCallback is a function that accepts a callback of type MyCallBack and optional parameters param1 (string) and param2 (number). It calls the callback function using the provided parameters.

Example 1: Define type MyCallback, where param2 is an optional parameter. The callback function takes two parameters, str (a string) and num (an optional number). Inside this function you record the received string and if num is provided you save that number as well. Otherwise, the number is not provided. The example calls callback myFunction twice: first with just the string parameter, then with both strings and numbers.

type MyCallback = (param1: string, param2?: number) => void; const myFunction: MyCallback = (str, num) => { console.log(`Received: ${str}`); if (num !== undefined) { console.log(`Number: ${num}`); } else { console.log("Number is not provided."); } }; // G?i callback có và không có tham s? tùy ch?n myFunction("GeeksforGeeks"); myFunction("A Computer Science Portal", 99); 

Result:

Example 2: Define the MathOperationCallback type for callback functions that implement mathematical operations on two numbers, with an optional description parameter. The performMathOperation function takes a callback function, two numbers (a and b), and adds an optional description parameter.

type MathOperationCallback = (a: number, b: number, description?: string) => number; function performMathOperation( operation: MathOperationCallback, a: number, b: number, description?: string ) { const result = operation(a, b); console.log(`Operation: ${description || "Unnamed"}`); console.log(`Result: ${result}`); } // Xác ??nh m?t hàm b? sung tùy bi?n const customAddition: MathOperationCallback = (x, y, description) => { const sum = x + y; console.log(`Performing addition: ${description || "Unnamed"}`); return sum; }; // Tri?n khai các phép tính // kèm ho?c không kèm mô t? // Không cung c?p mô t? performMathOperation(customAddition, 5, 3); // Kèm mô t? performMathOperation(customAddition, 10, 7, "Adding Numbers"); 

Result:

Hope this article helps you better understand callback optional parameters in TypeScript.