JS: Function Parameters

By Xah Lee. Date: 2014-06-30. Last updated: 2024-05-19.

Number of Arguments Not Checked

JavaScript doesn't check the number of arguments passed in a function call.

If there are more arguments passed in a function call than declared parameters, they are ignored.
If less, then extra parameter variables have values of undefined .

function ff(x) {
  return x;
}

// extra arguments are ignored
console.log(ff(2, 3, 4) === 2);

const gg = ((x) => x);

// extra arguments are ignored
console.log(gg(2, 3, 4) === 2);

// unfilled parameters have value of undefined
function gg(x, y) {
  return y;
}
console.log(gg(3) === undefined);

// unfilled parameters have value of undefined
const gg = ((x, y) => y);
console.log(gg(3) === undefined);

The total count of arguments passed is arguments.length.