Using rest parameters in JavaScript functions
Discover how to use rest parameters in JavaScript functions.
1 min read
The rest parameters syntax provides an easy way to pass an indefinite number of arguments to a function as an array. Rest parameters syntax allows a function to be called with any number of arguments, no matter how it was defined. Rest parameters syntax was added in ES2015 or ES6.
Let's define a function that uses rest parameters.
function sum(...values) {
let sum = 0;
for (let value of values) {
sum += value;
}
return sum;
}
console.log(sum(1)); // result is 1
console.log(fun(1, 2)); // result is 3
console.log(fun(1, 2, 3)); // result is 6
Rest parameters at the end
A function can have its first parameters as variables, and gather only the rest using the rest parameters syntax. The rest parameters must be the last entry in a function's parameters because they gather all remaining arguments.
function getFullName(firstName, lastName, ...titles) {
console.log(titles[0]); // CEO
console.log(titles[1]); // CIO
console.log(titles[2]); // COO
console.log(titles[3]); // undefined
console.log(titles.length); // 3
return `${firstName} ${lastName} - ${titles.join(', ')}`;
}
const fullName = getFullName('John', 'Smith', 'CEO', 'CIO', 'COO');
console.log(fullName); // John Smith - CEO, CIO, COO