Breaking out of a PrototypeJS .each() loop

Question

In this very contrived example, I have an array with 3 elements that I'm looping over using the .each() method.

var vals = $w('foo bar baz'); 

vals.each( function(val) {
    alert(val);

    if( val == 'bar' ) {
        //This exits function(val)
        //but still continues with the .each()
        return;
    }
});

I can easily return out of the function being called by .each() if I need to.

My question is, how can I break out of the .each() loop from inside the function that .each() is calling?

Solution 1

if( val == 'bar' ) {
    throw $break;
}

It's documented at the same page you linked. It's an exception specially handled by the each function. When thrown, it prevents your function from being called on further elements.

Solution 2

Your are correct, and Prototype has created an object ($break) that can be thrown from the each-function to enable this functionality. According to the Prototype API docs:

Regular loops can be short-circuited in JavaScript using the break and continue statements. However, when using iterator functions, your code is outside of the loop scope: the looping code happens behind the scene.

In order to provide you with equivalent (albeit less optimal) functionality, Prototype provides two global exception objects, $break and $continue. Throwing these is equivalent to using the corresponding native statement in a vanilla loop. These exceptions are properly caught internally by the each method.

Also, note that the $continue object has been deprecated, and to simulate a continue-statement, use a vanilla return statement instead.

Code example:

var result = [];
$R(1,10).each(function(n) {
  if (0 == n % 2)
    return; // this equals continue
  if (n > 6)
    throw $break;
  result.push(n);
});
// result -> [1, 3, 5]

You can read more about the each-function here: http://www.prototypejs.org/api/enumerable/each

Solution 3

Based on the documentation for .each() that you linked to, you should use a throw $break; statement, this should cause further iterations to cease.

Simply returning will cause the iterator to continue to the next one.

Solution 4

From that page you linked to, isn't the correct way

 if(val == 'bar')
 {
    throw $break;
 }

?

View more solutions

Comments

[Mark Biek]

Doh! Looks like there's a "throw $continue" too.

[Matthew Flaschen]

As noted there, $continue is deprecated and rather pointless. You can just return.

[Joel Mueller]

However, "throw $continue" is deprecated in favor of a simple return.

[llamerr]

I want to note that new docs page does not have this info now