JavaScript: Function Rest Parameters

New in JS2015.

A function can have unspecified number of parameters, like this:

function ff (...name) { return name; }

That is, 3 dots followed by a name. In function body, the name is received as a array.

This is called “rest parameters”.

The syntax ...name must be the last in the parameter declaration. Space after the dots is optional.

The syntax ...name can only happen once.

// function with any number of parameters
function ff (a, b, ...c)
{
return c; // c is received as array
};

console.log(
 ff(1,2,3,4)
); // [3, 4]

If no rest parameter is given, value is a empty array.

// rest params, if non given, value is empty array
function f1 (...r) { return r; };
console.log( f1() ); // []