JavaScript Iterators

Question

I was going through MDN (Mozilla Developer Network) and came across Iterators and generators

So naturally, I tried the snippets of code given in the page on Google Chrome v21. To be specific, this code:

var it = Iterator(lang);
for (var pair in it)
  print(pair); // prints each [key, value] pair in turn

However, the console returns this error message:

ReferenceError: Iterator is not defined

Why's that? Is the Iterator function deprecated or something? Am I missing a point? Thank you for your help and time :-)

Somewhat related: [Google Chrome - javascript version](http://stackoverflow.com/questions/300185/google-chrome-javascript-version) — j.w.r, Aug 22 '12 at 18:46

score 6 · Answer 1 · answered Jan 04 '13 at 21:54

Arrays have a built in map function that acts like an iterator.

[1,2,3].map(function(input){console.log(input)});

Standard Out:

1
2
3

Worst case you could easily design an iterator object, didn't full test this but if there are any bugs you should be able to quickly get this working.

var Iterator = function(arr){ return {
    index : -1,
    hasNext : function(){ return this.index <= arr.length; },
    hasPrevious: function(){ return this.index > 0; },

    current: function(){ return arr[ this["index"] ]; },

    next : function(){
        if(this.hasNext()){
            this.index = this.index + 1;            
            return this.current();
        } 
        return false;
    },

    previous : function(){
        if(this.hasPrevious()){
            this.index = this.index - 1
            return this.current();
        }
        return false;
    }
}   
};

var iter = Iterator([1,2,3]);

while(iter.hasNext()){
    console.log(iter.next());
}

Maybee hasNext : function(){ return this.index < arr.length-1; }, ? — zloctb, Jun 29 '14 at 10:46

score 4 · Answer 2 · answered Aug 22 '12 at 18:45

4

window.Iterator AFAIK only exists in Firefox, not WebKit.

answered Aug 22 '12 at 18:45

David Hellsing

106,495
44
176
212

score 3 · Accepted Answer · edited Jun 20 '20 at 09:12

From this thread:

V8 is an implementation of ECMAScript, not JavaScript. The latter is a non-standardized extension of ECMAScript made by Mozilla.

V8 is intended to be plug-in compatible with JSC, the ECMAScript implementation in WebKit/Safari. As such it implements a number of non-standard extensions of ECMAScript that are also in JSC, and most of these are also in Mozilla's JavaScript languages.

There is no plan to add non-standard features that are not in JSC to V8.

Note: JSC stands for JavaScript Core - the WebKit ECMAScript implementation.

score 2 · Answer 4 · answered Jul 07 '14 at 07:47

var makeIterator = function (collection, property) {
    var agg = (function (collection) {
    var index = 0;
    var length = collection.length;

    return {
      next: function () {
        var element;
          if (!this.hasNext()) {
            return null;
          }
          element = collection[index][property];
          index = index + 1;
          return element;
        },
      hasNext: function () {
        return index < length;
      },
      rewind: function () {
        index = 0;
      },
      current: function () {
        return collection[index];
      }
    };
 })(collection);

 return agg;
};


var iterator = makeIterator([5,8,4,2]);

console.log(iterator.current())//5
console.log(  iterator.next() )
console.log(iterator.current()) //8
console.log(iterator.rewind());
console.log(iterator.current()) //5

score 1 · Answer 5 · answered Aug 22 '12 at 18:47

1

It means that Chrome v21 does not support that feature of JavaScript. It's part of the 1.7 spec. Trying this might help for specifying explicitly 1.7 support in Chrome.

answered Aug 22 '12 at 18:47

Mike Thomsen

36,828
10
60
83

score 0 · Answer 6 · answered Mar 21 '15 at 08:50

0

For chrome you could use this

var someArray = [1, 5, 7];
var someArrayEntries = someArray.entries();

here is link, which you could find interesting

answered Mar 21 '15 at 08:50

andrey

347
3
11

JavaScript Iterators

6 Answers6

Linked