call by value

function increment_1(a){
  a = 100;
}

function increment_2(a){
  a = 100;
  return a;
}

let c = 3;
console.log(increment_1(c)); // undefined
console.log(c); // 3
console.log(increment_2(c)); // 100

function append(array, value){
  array.push(value)
}

let array = [1, 2];
append(array, 3);

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