javascript - Is there a difference between a function with and without a return statement? - Stack Overflow

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Say you have 2 identical functions that do not return a value

function a() {
    // do some interesting things
}

function b() {
    // do the same interesting things
    return;
}

Function b is obviously more verbose but is there any functional difference between these?

Say you have 2 identical functions that do not return a value

function a() {
    // do some interesting things
}

function b() {
    // do the same interesting things
    return;
}

Function b is obviously more verbose but is there any functional difference between these?

• javascript

Share Follow edited Feb 24, 2012 at 18:13 pimvdb 155k8080 gold badges311311 silver badges356356 bronze badges asked Feb 24, 2012 at 18:02 Matt CampbellMatt Campbell 25322 silver badges1010 bronze badges 3

• 2 A good answer to this should include a link to the relevant part of the ECMA spec. – georg Commented Feb 24, 2012 at 18:04
• 2 return; basically means terminate function here. So if you have it as the last bit of your function it does not do anything useful. – gintas Commented Feb 24, 2012 at 18:09
• 1 12.9 in the spec, for those interested. – davin Commented Feb 24, 2012 at 18:50

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3 Answers 3

Sorted by: Reset to default 11

There's no real difference; both will return undefined.

Functions with no return statement will return undefined, as will functions with an empty return statement.

---

To confirm this for yourself, you can run this code -- FIDDLE:

​function a() {
}

function b() {
    return;
}

var aResult = a();
var bResult = b();

alert(aResult === bResult);  //alerts true

Adam is correct; both functions return undefined, and either way is absolutely fine if you don't care about the return value (or desire the value to be undefined). However, it's often better in more plex programs to explicitly return from a function, especially since Javascript programs often have plex callback mechanisms. For example, in this piece of code (just a little more plex than yours) I believe the return statement really helps clarify the code:

function someAsyncFunction(someVar, callback) {
    // do something, and then...
    callback(someVar);
    // will return undefined
    return;
}

function c(){
    var someState = null;
    if (some condition) {
        return someAsyncFunction(some variable, function () {
            return "from the callback but not the function";
        });
        // we've passed the thread of execution to someAsyncFunction
        // and explicitly returned from function c.  If this line
        // contained code, it would not be executed.
    } else if (some other condition) {
         someState = "some other condition satisfied";
    } else {
         someState = "no condition satisfied";
    }
    // Note that if you didn't return explicitly after calling
    // someAsyncFunction you would end up calling doSomethingWith(null)
    // here.  There are obviously ways you could avoid this problem by
    // structuring your code differently, but explicit returns really help
    // avoid silly mistakes like this which can creep into plex programs.
    doSomethingWith(someState);
    return;
}

// Note that we don't care about the return value.
c();

Generally you are returning a value. So for instance,

function b() {
  return 'hello';
}

a = b();

console.log(a);

Will output "hello" to your console.

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