The legacy Iterator protocol
Non-standard. The legacy iterator protocol is a SpiderMonkey-specific feature, and will be removed at some point. For future-facing usages, consider using for..of loops and the iterator protocol.
The deprecated Firefox-only iterator protocol
Firefox, prior to version 26 implemented another iterator protocol that is similar to the standard ES2015 Iterator protocol.
An object is an legacy iterator when it implements a next()
method with the following semantics, and throws StopIteration
at the end of iteration.
Property | Value |
---|---|
next |
A zero arguments function that returns an value. |
Difference between legacy and ES2015 iterator protocols
- The value was returned directly as a return value of calls to
next
, instead of thevalue
property of a placeholder object - Iteration termination was expressed by throwing a
StopIteration
object.
Simple example with the old protocol
JavaScript
Copy Code
function makeIterator(array){ var nextIndex = 0; return { next: function(){ if(nextIndex < array.length){ return array[nextIndex++]; else throw new StopIteration(); } } } var it = makeIterator(['yo', 'ya']); console.log(it.next()); // 'yo' console.log(it.next()); // 'ya' try{ console.log(it.next()); } catch(e){ if(e instanceof StopIteration){ // iteration over } }
See also
License
© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-us/docs/web/javascript/reference/deprecated_and_obsolete_features/the_legacy_iterator_protocol