Rest

Array Rest

Rest parameters are the equivalent for variadic parameters in some other languages.

The add function below can take any number of parameters which will end up in the valueList Array.

const add = (...valueList) => {
    return valueList.reduce((total, value) => total + value, 0);
};

add(0, 1, 2, 3); // 6

It is better to avoid the usage of "rest" parameters. It reduces the extensibility of the function. It is better to use one parameter of type Array that contains all the values.

const add = (valueList) => {
    return valueList.reduce((total, value) => total + value, 0);
};

add([1, 2, 3]); // 6

Object Rest

The same syntax can be used with the destructuring of an object.

const user = {
    firstName: 'Foo',
    lastName: 'BAR',
    email: '[email protected]',
    phoneNumber: '123'
};

const { firstName, lastName, ...remainingProperties } = user;

console.log(remainingProperties); // { email: '[email protected]', phoneNumber: '123' }