JavaScript Iterator Class

Question

Do you know a JavaScript library that implements a generic Iterator class for collections (be it Arrays or some abstract Enumerable) with a full set of features, like the Go

Answer 1

In the time since this question was asked JavaScript has added actual Iterators. Some built-in types, such as Array, Map, and String now have a default iteration behavior, but you can add your own to any object by including a next() function which returns one of two objects:

{done:true}     /*or*/
{done:false, value:SOMEVALUE}

One way to access an object Iterator is with the:

for ( var of object ) { }

loop. Here is a (reasonably silly) example where we define an Iterator and then use it in such a loop to produce a string 1, 2, 3:

"use strict";

function count ( i ) {
  let n = 0;
  let I = {};
  I[Symbol.iterator] = function() {
     return { next: function() { return (n > i) ? {done:true}
                                                : {done:false, value:n++} } } };
  let s = "";
  let c = "";
  for ( let i of I ) {       /* use the iterator we defined above */
      s += c + i;
      c = ", "
  }
  return s;
}


let s = count(3);
console.log(s);