Functions

Define once, use many times

A function is a named block of code you can run whenever you want. Define it with function, then call it with its name and ().

<script>
  function greet() {
    document.write("Hello, CodingClave!<br>");
  }
  greet();   // call it
  greet();   // call again
</script>

The function greet() { ... } part only defines the recipe — nothing happens yet. Each greet() line below actually runs it. Because we call it twice, the message is written twice.

Parameters and return

Parameters let you pass data in. return sends a result back out.

<script>
  function add(a, b) {
    return a + b;
  }
  let result = add(5, 3);
  document.write("5 + 3 = " + result);
</script>

add has two parameters, a and b — empty slots for incoming numbers. When we call add(5, 3), a becomes 5 and b becomes 3, and return a + b sends 8 back. That returned 8 lands in result, which we then print.

The real power is reuse: the same function gives different answers for different inputs.

<script>
  function greet(name) {
    return "Hello, " + name + "!";
  }
  document.write(greet("Asha") + "<br>");
  document.write(greet("Ravi"));
</script>

greet("Asha") runs the function with name set to "Asha", returning "Hello, Asha!". The second call passes "Ravi", returning "Hello, Ravi!". One recipe, two different results — that is why functions save so much repeated typing.