Does Every JavaScript Function Require a Return Value?

While the title suggests that all JavaScript functions must return a value, the matter is slightly more nuanced.

Short Answer: No

JavaScript functions are not obligated to explicitly return a value.

Longer Explanation

However, the JavaScript engine does expect a function to indicate its completion, which is usually achieved through a return statement. Whether explicit or implicit, every function returns something.

For instance, if a function lacks an explicit return statement, it defaults to returning undefined. This behavior mirrors that of C functions with a void return type.

Here's an example:

function noReturn() {
    console.log('123'); // Log to the console, but don't return anything
}

// This function will return undefined, even though the return statement is omitted
const result = noReturn();

While you can ignore the return value, it's considered good practice to explicitly indicate the intended behavior. Undefined return values can lead to unexpected outcomes in some cases.

Despite the seeming lack of obligation, all JavaScript functions effectively return something, either explicitly through a return statement or implicitly by returning undefined. This behavior ensures that the engine and event handlers know when and what to execute next.