parameters in javascript

1function foo() {
2  for (var i = 0; i < arguments.length; i++) {
3    console.log(arguments[i]);
4  }
5}
6
7foo(1,2,3);
8//1
9//2
10//3

1function sum(...values) {
2    console.log(values);
3}
4sum(1);
5sum(1, 2);
6sum(1, 2, 3);
7sum(1, 2, 3, 4);
8
9
10function sum(...values) {
11    let sum = 0;
12    for (let i = 0; i < values.length; i++) {
13        sum += values[i];
14    }
15  
16    return sum;
17}
18console.log(sum(1)); //1
19console.log(sum(1, 2)); //3
20console.log(sum(1, 2, 3)); // 5
21console.log(sum(1, 2, 3, 4)); //10

1function functionName(parameter1, parameter2, parameter3) {}

1function myFunction(x, y) {
2  if (y === undefined) {
3    y = 2;
4  }
5}