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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 ES6 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 ES6 iterator protocols
- The value was returned directly as a return value of calls to
next, instead of thevalueproperty of a placeholder object - Iteration termination was expressed by throwing a
StopIterationobject.
Simple example with the old protocol
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
}
}