JavaScript functions: parameters and return

A function writes one job once and runs it many times. After function come the name, then () and {}. Writing it does not run it. It runs when you write the name and (). If you forget the parentheses, nothing happens.

function seslen() {
  console.log("Burdayam");
}
seslen();

function yazdir(ad) {
  console.log(ad);
}
yazdir("Əli");

A parameter is information given to the function. return sends a result back and stops the function on that line. console.log only prints. It does not keep the value. If the second parameter is missing, the result is NaN.

function topla(a, b) {
  return a + b;
}
console.log(topla(4, 6)); // 10

function yoxla(bal) {
  if (bal >= 50) return "Keçdi";
  return "Kəsildi";
}
console.log(yoxla(40));

An array can be a parameter too. Inside, a for loop can find the sum and the largest number. If {} is not closed, you get an error. The line after return does not run.

function massivCemi(ededler) {
  let cem = 0;
  for (let i = 0; i < ededler.length; i++) {
    cem = cem + ededler[i];
  }
  return cem;
}
console.log(massivCemi([1, 2, 3, 4])); // 10

function enBoyuk(ededler) {
  let max = ededler[0];
  for (let i = 1; i < ededler.length; i++) {
    if (ededler[i] > max) max = ededler[i];
  }
  return max;
}

Why does a function not run by itself? You must call it: seslen(). Writing only the name, without parentheses, is not enough.

What is the difference between console.log and return? console.log shows. return gives the value back so you can keep it somewhere else.

Why does code after return not run? return stops the function. The line after it is not read.

What if I pass one number to a function with two parameters? The second is undefined and the sum is NaN. Pass every parameter.