TypeScript Rest Parameters

In this tutorial, you will learn about the TypeScript rest parameters that allows you to represent an indefinite number of arguments as an array.

A rest parameter allows you a function to accept zero or more arguments of the specified type. In TypeScript, rest parameters follow these rules:

1. A function has only one rest parameter.
2. The rest parameter appears last in the parameter list.
3. The type of the rest parameter is an array type.

To declare a rest parameter, you prefix the parameter name with three dots and use the array type as the type annotation:

function fn(...rest: type[]) {
   //...
}

The following example shows how to use the rest parameter:

function getTotal(...numbers: number[]): number {
    let total = 0;
    numbers.forEach((num) => total += num);
    return total;
}

In this example, the getTotal() calculates the total of numbers passed into it.

Since the numbers parameter is a rest parameter, you can pass one or more numbers to calculate the total:

console.log(getTotal()); // 0
console.log(getTotal(10, 20)); // 30
console.log(getTotal(10, 20, 30)); // 60

In this tutorial, you have learned about the TypeSript rest parameters that allow you to represent an indefinite number of arguments as an array.