How is array map working without passing the parameter?

const arr2 = arr.map(double)

How this is working without me passing the array item? I need to pass a parameter to function double: something like double(item).

let arr = [1, 2, 3, 4, 5]

function double(x) {
  return x * 2
}

const arr2 = arr.map(double)

const arr3 = arr.map(item => double(item))

console.log("arr2= ", arr2)
console.log("arr3= ", arr3)

Output:

arr2 = [2, 4, 6, 8, 10]

arr3 = [2, 4, 6, 8, 10]