Early exit from function?

I have a function:

function myfunction() {
  if (a == 'stop')  // How can I stop the function here?
}

Is there something like exit() in JavaScript?

You can just use return.

function myfunction() {
     if(a == 'stop') 
         return;
}

This will send a return value of undefined to whatever called the function.

var x = myfunction();

console.log( x );  // console shows undefined

Of course, you can specify a different return value. Whatever value is returned will be logged to the console using the above example.

return false;
return true;
return "some string";
return 12345;