将自定义迭代器添加到javascript类

Question

我试图找出如何将一个迭代器添加到javascript类,以便该类可以在for ... in循环中使用.遵循Mozilla的指示不会产生他们声称的结果. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Iterators_and_Generators 给出示例的Jsfiddle:http://jsfiddle.net/KQayW/

function Range(low, high){
  this.low = low;
  this.high = high;
  this.current = low;
  this.next = function() {
    if (this.current > this.range.high)
      throw StopIteration;
    else
      return this.current++;
  }
}
function RangeIterator(range){
  this.range = range;
  this.current = this.range.low;
}
RangeIterator.prototype.next = function(){
  if (this.current > this.range.high)
    throw StopIteration;
  else
    return this.current++;
};
Range.prototype.__iterator__ = function(){
  return new RangeIterator(this);
};
var range = new Range(3, 5);
for (var i in range)
  document.getElementById("test").innerHTML = i+"</br>"; // prints 3, then 4, then 5 in sequence

它不打印范围内的数字,它打印出"__iterator__"!

有谁知道如何让这个工作？

Answer 1

使用ES2015简单:

function Range(start, end) {
    var ret = {};
    ret[Symbol.iterator] = function *() {
        while (start < end) 
            yield start++;
    }
    return ret;
}

虽然你必须使用:

for (var x of Range(1, 10))

Answer 2

使用 ES2015 可以更简单

const Range = (start, end) => ({
  *[Symbol.iterator]() {
    while (start < end) 
        yield start++;
  }
})

for (var x of Range(1, 10)) {
  console.log(x)
}

Answer 3

Mozilla 文档指出，迭代器功能是在 JavaScript 1.7 中引入的。尽管 Chrome 从 1.7 开始就支持一些功能，但并未完全支持，因此这不起作用。如果您在最新的 Firefox 版本中测试您的代码，您会发现它可以工作。

尽管您可能想要附加范围值而不是替换整个 div。

http://jsfiddle.net/KQayW/2/

function Range(low, high){
  this.low = low;
  this.high = high;
  this.current = low;
  this.next = function() {
  if (this.current > this.range.high)
    throw StopIteration;
  else
    return this.current++;
  }
}
function RangeIterator(range){
  this.range = range;
  this.current = this.range.low;
}
RangeIterator.prototype.next = function(){
  if (this.current > this.range.high)
    throw StopIteration;
  else
    return this.current++;
};
Range.prototype.__iterator__ = function(){
  return new RangeIterator(this);
};
var range = new Range(3, 5);
for (var i in range)
  document.getElementById("test").innerHTML += i+"</br>"; // prints 3, then 4, then 5 in sequence