Question

你知道一个JavaScript库，它为集合实现一个通用的Iterator类（可以是Arrays还是一些抽象的Enumerable），它具有一整套功能，比如Google Common或Apache Commons？

编辑：Enumerable#each不是Iterator类。我正在寻找一个迭代器，它可以让我们写出类似的东西：

var iterator = new Iterator(myCollection);
for (var element = iterator.next(); iterator.hasNext(); element = iterator.next()) {
    // iterator 
}

编辑：mamoo提醒我们Mozilla's Javascript 1.7中的迭代器实现。所以现在的目标是在Javascript 1.5（ECMA 4）中找到这个Iterator函数的实现。

Edit2：为什么在库（和ECMA 5）提供each方法时使用迭代器？首先，因为each通常与this混淆，因为回调是call -ed（这就是为什么each接受Prototype中的第二个参数）。然后，因为人们对for(;;)构造比对.each(callback)构造更熟悉（至少在我的领域）。最后，因为迭代器可以遍历普通对象（参见JavaScript 1.7）。

Edit3：我接受了npup的anwser，但这是我的镜头：

function Iterator(o, keysOnly) {
    if (!(this instanceof arguments.callee))
      return new arguments.callee(o, keysOnly);
    var index = 0, keys = [];
    if (!o || typeof o != "object") return;
    if ('splice' in o && 'join' in o) {
        while(keys.length < o.length) keys.push(keys.length);
    } else {
        for (p in o) if (o.hasOwnProperty(p)) keys.push(p);
    }
    this.next = function next() {
        if (index < keys.length) {
            var key = keys[index++];
            return keysOnly ? key : [key, o[key]];
        } else throw { name: "StopIteration" };
    };
    this.hasNext = function hasNext() {
        return index < keys.length;
    };
}



var lang = { name: 'JavaScript', birthYear: 1995 };  
var it = Iterator(lang);
while (it.hasNext()) {
    alert(it.next());
}
//alert(it.next()); // A StopIteration exception is thrown  


var langs = ['JavaScript', 'Python', 'C++'];  
var it = Iterator(langs);
while (it.hasNext()) {
    alert(it.next());
}
//alert(it.next()); // A StopIteration exception is thrown

Answer 1

JQuery有each（）方法： http://api.jquery.com/jQuery.each/

但即使在Moo或Dojo等其他库中也可能有类似内容。

Javascript 1.7实现了Iterator功能： https://developer.mozilla.org/en/Core_JavaScript_1.5_Guide/Iterators_and_Generators

Answer 2

好的，可枚举模式不是真正的迭代器。

这（下面）对你有用吗？它符合你至少给出的语义。像往常一样，在这里和那里都要做出权衡，在决定这个时候我并没有想到很多:) 也许你希望能够发送一两个数字并以这种方式迭代一个范围。但这可能是一个开始（支持迭代哈希，数组和字符串）。

这是一个完整的演示页面，它自己运行并进行一些调试输出，但（可能）有趣的东西在

window.npup = (function() {
    [...]
})();

点。

也许只是我根本没有得到它，但你会在真实情况下使用这种类似java的迭代器？

最佳

/ npup

<html>
<head>
<title>untitled</title>
</head>

<body>
    <ul id="output"></ul>


<script type="text/javascript">
window.log = (function (outputAreaId) {
    var myConsole = document.getElementById(outputAreaId);
    function createElem(color) {
        var elem = document.createElement('li');
        elem.style.color = color;
        return elem;
    }
    function appendElem(elem) {
        myConsole.appendChild(elem);
    }
    function debug(msg) {
        var elem = createElem('#888');
        elem.innerHTML = msg;
        appendElem(elem);
    }
    function error(msg) {
        var elem = createElem('#f88');
        elem.innerHTML = msg;
        appendElem(elem);
    }
    return {
        debug: debug
        , error: error
    };
})('output');


window.npup = (function () {
    // Array check as proposed by Mr. Crockford
    function isArray(candidate) {
        return candidate &&
            typeof candidate==='object' &&
            typeof candidate.length === 'number' &&
            typeof candidate.splice === 'function' &&
            !(candidate.propertyIsEnumerable('length'));
    }
    function dontIterate(collection) {
        // put some checks chere for stuff that isn't iterable (yet)
        return (!collection || typeof collection==='number' || typeof collection==='boolean');
    }
    function Iterator(collection) {
        if (typeof collection==='string') {collection = collection.split('');}
        if (dontIterate(collection)) {throw new Error('Oh you nasty man, I won\'t iterate over that ('+collection+')!');}
        var arr = isArray(collection);
        var idx = 0, top=0;
        var keys = [], prop;
        if (arr) {top = collection.length;}
        else {for (prop in collection) {keys.push(prop);}}
        this.next = function () {
            if (!this.hasNext()) {throw new Error('Oh you nasty man. I have no more elements.');}
            var elem = arr ? collection[idx] : {key:keys[idx], value:collection[keys[idx]]};
            ++idx;
            return elem;
        };
        this.hasNext = function () {return arr ? idx<=top : idx<=keys.length;};
    }
    return {Iterator: Iterator};
})();

var element;

log.debug('--- Hash demo');
var o = {foo:1, bar:2, baz:3, bork:4, hepp: {a:1,b:2,c:3}, bluff:666, bluff2:777};
var iterator = new npup.Iterator(o);
for (element = iterator.next(); iterator.hasNext(); element = iterator.next()) {
    log.debug('got elem from hash: '+element.key+' => '+element.value);
    if (typeof element.value==='object') {
        var i2 = new npup.Iterator(element.value);
        for (var e2=i2.next(); i2.hasNext(); e2=i2.next()) {
            log.debug('&nbsp;&nbsp;&nbsp;&nbsp;# from inner hash: '+e2.key+' => '+e2.value);
        }
    }
}
log.debug('--- Array demo');
var a = [1,2,3,42,666,777];
iterator = new npup.Iterator(a);
for (element = iterator.next(); iterator.hasNext(); element = iterator.next()) {
    log.debug('got elem from array: '+ element);
}
log.debug('--- String demo');
var s = 'First the pants, THEN the shoes!';
iterator = new npup.Iterator(s);
for (element = iterator.next(); iterator.hasNext(); element = iterator.next()) {
    log.debug('got elem from string: '+ element);
}
log.debug('--- Emptiness demo');
try {
    log.debug('Try to get next..');
    var boogie = iterator.next();
}
catch(e) {
    log.error('OW: '+e);
}

log.debug('--- Non iterables demo');
try{iterator = new npup.Iterator(true);} catch(e) {log.error('iterate over boolean: '+e);}
try{iterator = new npup.Iterator(6);} catch(e) {log.error('iterate over number: '+e);}
try{iterator = new npup.Iterator(null);} catch(e) {log.error('iterate over null: '+e);}
try{iterator = new npup.Iterator();} catch(e) {log.error('iterate over undefined: '+e);}

</script>
</body>
</html>

Answer 3

这是我对ECMAScript 262第5版（又名Javascript）的尝试（jsfiddle）。（例如使用Object.keys和Array.isArray）

//Usage
b=Iterator(a);
while(b()){
  console.log(b.value);
}

代码：

function Iterator(input,keys) {
  // Input:
  //  input : object|array
  //  keys   : array|undefined|boolean
  function my() {
    ++my.index;
    if (my.index >= my.keys.length) {
      my.index = my.keys.length -1;
      my.key = my.value = undefined;
      return false;
    }
    my.key = my.useIndex ? my.index : my.keys[my.index];
    my.value = my.input[my.key];
    return my.index < my.keys.length;
  }
  if (input === null || typeof input !== 'object') {
    throw new TypeError("'input' should be object|array");
  }
  if (
    !Array.isArray(keys)
    && (typeof keys !== 'undefined')
    && (typeof keys !== 'boolean')
    ) {
    throw new TypeError("'keys' should be array|boolean|undefined");
  }
  // Save a reference to the input object.
  my.input = input;
  if (Array.isArray(input)) {
    //If the input is an array, set 'useIndex' to true if 
    //the internal index should be used as a key.
    my.useIndex = !keys;
    //Either create and use a list of own properties,
    // or use the supplied keys
    // or at last resort use the input (since useIndex is true in that
    // case it is only used for the length)
    my.keys = keys===true ? Object.keys(input) : keys || input;
  } else {
    my.useIndex = false;
    my.keys = Array.isArray(keys) ? keys : Object.keys(input);
  }
  // Set index to before the first element.
  my.index = -1;
  return my;
}

示例：

function Person(firstname, lastname, domain) {
  this.firstname = firstname;
  this.lastname = lastname;
  this.domain = domain;
}
Person.prototype.type = 'Brillant';

var list = [
  new Person('Paula','Bean','some.domain.name'),
  new Person('John','Doe','another.domain.name'),
  new Person('Johanna','Doe','yet.another.domain.name'),
];

var a,b; 
var data_array = ['A','B','C','D','E','F'];
data_array[10]="Sparse";


console.log('Iterate over own keys in an object, unknown order');
a = Iterator(list[0]);
while(a()) console.log("  ",a.key, a.value);

console.log('Iterate over keys from anywhere, in specified order');
a = Iterator(list[0], ['lastname','firstname','type']);
while(a()) console.log("  ",a.key, a.value);

console.log('Iterate over all values in an array');
a = Iterator(list);
while(a()) console.log(a.key, a.value.firstname, a.value.lastname);


//Some abusing, that works for arrays (if the iterator.keys is modified
//it can also be used for objects)
console.log('Add more entries to the array, reusing the iterator...');
list.push(new Person('Another','Name','m.nu'));
while(a()) console.log(a.key, a.value.firstname, a.value.lastname);

console.log('Reset index and print everything again...');
a.index=-1; //Reset the index.
while(a()) console.log(a.key, a.value.firstname, a.value.lastname);

//With arrays, if setting 'keys' to true it will only print the
//elements that has values (If the array has more own enumerable values
//they too will be included)
console.log('Print sparce arrays...');
a = Iterator(data_array,true);
while(a()) console.log(a.key, a.value);

Answer 4

自提出此问题以来，JavaScript已添加实际Iterators。某些内置类型（例如Array，Map和String）现在具有默认的迭代行为，但您可以通过包含next()将自己的类型添加到任何对象返回两个对象之一的函数：

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

访问对象迭代器的一种方法是：

for ( var of object ) { }

环。这是一个（相当愚蠢的）示例，我们定义一个Iterator，然后在这样的循环中使用它来生成一个字符串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);

Answer 5

我在一些项目中使用了LINQ to Javascript。

http://jslinq.codeplex.com/Wikipage

var myList = [
            {FirstName:"Chris",LastName:"Pearson"},
            {FirstName:"Kate",LastName:"Johnson"},
            {FirstName:"Josh",LastName:"Sutherland"},
            {FirstName:"John",LastName:"Ronald"},
            {FirstName:"Steve",LastName:"Pinkerton"}
            ];

var exampleArray = JSLINQ(myList)
                   .Where(function(item){ return item.FirstName == "Chris"; })
                   .OrderBy(function(item) { return item.FirstName; })
                   .Select(function(item){ return item.FirstName; });

Answer 6

我仍然是js.class的学习者。虽然接近Ruby，但帮助我。

http://jsclass.jcoglan.com/enumerable.html

MARKT

Answer 7

由于尚未提及数组内置的高阶函数。

Map就像迭代器一样，只能执行一次传递。

[1,2,3,4,5].map( function(input){ console.log(input); } );

此代码将列表中的每个元素传递给一个函数，在本例中是一个简单的打印机。

JavaScript Iterator类

7 个答案: