Array.prototype.reduce().gs

function myFunction() {
  const array1 = [1, 2, 3, 4];
//  const reducer = (accumulator, currentValue) => accumulator + currentValue;
  const reducer = function(accumulator, currentValue) { return accumulator + currentValue;};

  // 1 + 2 + 3 + 4
  console.log(array1.reduce(reducer));
  // expected output: 10
  
  // 5 + 1 + 2 + 3 + 4
  console.log(array1.reduce(reducer, 5));
  // expected output: 15
}