Understand the idea

A function groups work that can be called with different inputs. Parameters name the inputs; arguments are the values supplied when calling it.

return sends a result back to the caller and stops the function. Logging a value displays it in the console but does not return it. Keep a function focused so that its purpose can be explained in one sentence.

Read the example

This is a JavaScript fragment. Run it in a browser console or an external script. Supply any HTML or data file named in the example first.

JavaScript · EXAMPLE
function describePhotos(count) {
  return count === 1 ? "1 photograph" : `${count} photographs`;
}
const label = describePhotos(3);
console.log(label);

A small mistake, explained

What goes wrong

A function without an executed return statement returns undefined. console.log inside the function does not change that.

How to fix it. Return the value needed by the caller, and keep any display or logging step separate.

Try it yourself

Test the function with 0, 1 and 3. Then write a simpler version using if and else instead of the conditional operator.

Further reading

ECMAScript — function definitions

Original explanation and example prepared for HTML code FYI with AI assistance. Test the code in your own context. How these guides are made.