Why should you care?

Without functions you copy-paste the same logic everywhere. One bug fix then means editing ten places.

See it live — copy this example

Paste into an HTML file or the browser console (F12). Use Run below when the live editor is available.

function greet(name) {
  return "Hello, " + name + "!";
}

console.log(greet("Sandeep"));
console.log(greet("Anita"));

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

What happened?

• function greet(name) declares a function with one parameter.
• return sends a value back to the caller.
• greet("Sandeep") calls the function with an argument.

Practice next

1. Run greet with different names.
2. Add function add(a, b) { return a + b; } and test it.
3. Call greet() with no argument and note undefined.
4. Give greet a default parameter: name = "Guest".
5. Return an object from a function that builds a user profile.

Remember

function name(params) { ... return value; } Call with name(arg) Parameters are placeholders; arguments are real values

ScriptVerse invoice formatter

formatCurrency(amount) is reused in cart, receipts, and admin reports instead of duplicating formatting logic.

Outcome: Functions centralize business rules so one fix updates every screen.