Typescript Rest Parameters

Typescript rest parameters

Created By: chatGPT

Rest parameters allow us to pass a variable number of arguments to a function. Instead of defining multiple parameters explicitly, we can use a single parameter prefixed with ... to handle any number of arguments as an array.

function sum(...numbers: number[]): number {
    return numbers.reduce((total, num) => total + num, 0);
}

const total = sum(1, 2, 3, 4, 5);
console.log(total); // Output: 15

In the example above, the sum function uses rest parameters to collect all arguments into the numbers array. The reduce method is then used to compute the total.

function concatenateStrings(...strings: string[]): string {
    return strings.join(' ');
}

const result = concatenateStrings('Hello', 'World', 'from', 'TypeScript');
console.log(result); // Output: Hello World from TypeScript

We can also combine rest parameters with other parameters. For instance, we can accept a fixed set of parameters before the rest parameter.

function greet(greeting: string, ...names: string[]): string {
    return `${greeting}, ${names.join(', ')}!`;
}

const greetingMessage = greet('Hello', 'Alice', 'Bob', 'Charlie');
console.log(greetingMessage); // Output: Hello, Alice, Bob, Charlie!

It's important to remember that rest parameters must be the last parameter in a function's parameter list. You can't place other parameters after it.

function invalidFunction(...args: any[], lastArg: number) {
    // This will throw an error
}

// Correct usage
function validFunction(lastArg: number, ...args: any[]) {
    // This is valid
}

In summary, rest parameters provide a flexible way to work with a variable number of arguments in TypeScript, enhancing the expressiveness of your functions.

const numbersOnly = sum(10, 20, 30);
const mixedParams = concatenateStrings('Data', 'Types', 'in', 'JavaScript', 'and', 'TypeScript');