CODEWITHSUNDEEP
javascript
FurtiveFelon
FurtiveFelon

Reputation: 15176

What does javascript function return in the absence of a return statement?

I was just wondering, does a function without a return statement (or without hitting any return statements) return a value that is completely equivalent to false?

For example:

function foo(){};
!!foo();

This should return false if executed in firebug (but does not return anything if i just called foo();).

Thanks a lot!

Jason

Upvotes: 61

Views: 23169

Answers (3)

Scott Evernden
Scott Evernden

Reputation: 39986

to find out, try this in firebug console:

alert((function(){})());

Upvotes: 0

user181548
user181548

Reputation: 

<html>
<body>
<script>
function a() {}
alert(a());
</script>
</body>
</html>

Upvotes: 2

Christian C. Salvad&#243;
Christian C. Salvad&#243;

Reputation: 827842

A function without a return statement (or one that ends its execution without hitting one) will return undefined.

And if you use the unary negation operator twice on an undefined value, you will get false.

You are not seeing anything on the console because Firebug doesn't prints the result of an expression when it's undefined (just try typing undefined; at the console, and you will see nothing).

However if you call the console.log function directly, and you will be able to see it:

function foo(){}

console.log(foo()); // will show 'undefined'

Upvotes: 78

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