Understanding the Return Statement in Javascript

A crucial aspect of understanding JavaScript programming involves being able to correctly interpret the return statement. One commonly encountered question is: What will happen if the return statement doesn’t have the associated expression? Contrary to what some might think, it does not throw an exception, nor does it return 0. Instead, it actually returns undefined.

function noReturn() {
    return;
}

console.log(noReturn()); 
// Output: undefined

In the example above, the function noReturn() contains a return statement without an associated expression. When we call the function and log its result, the output is undefined. This happens because, in JavaScript, a function without a return statement or a return without an expression implicitly returns undefined.

This is in line with JavaScript's philosophy of being a loosely typed language, where operations that might throw errors in other languages (like not returning a value in a function) are allowed.

However, it's considered good practice to always explicitly return a value from a function, if a value is expected. Implicitly returning undefined can sometimes lead to confusion or unexpected behavior, as it might not be immediately clear to others (or even your future self) why the function doesn't return a value. It's also easier to debug a function when its return behavior is explicitly defined.

Additionally, always returning a value from a function can often make the flow of data in your program easier to understand. The returned values can be used for further operations, logged for debugging, or tested in your unit tests to verify correct functionality.

In conclusion, while JavaScript allows return statements without associated expressions and will simply return undefined when they're encountered, using them is not generally recommended. Always aim to be explicit with your return statements for better readability, understandability, and maintainability of your code.