In what case and for what purpose is the 'undefined' value used in JavaScript as a return result of a function?

In JavaScript, the value undefined is often used as a return value of a function when the function does not explicitly return any value. This can be useful to indicate the absence of a result or when the function performs side effects but should not return data.

Examples of using undefined:

• The function does not contain a return statement or has a return without a value — by default, it returns undefined.
• Explicitly returning undefined to signal that the result is absent or not applicable.
• Used to check whether a parameter was passed or a calculation result.

Example:

function logMessage(msg) {
  console.log(msg);
  // No return, the function returns undefined
}

const result = logMessage('Hello');
console.log(result); // undefined

Thus, undefined serves as an indicator of the absence of a value or result.