Als*_*nde 16 javascript iterator
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不是迭代器类.我正在寻找一个Iterator,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的Javascript 1.7中的Iterator实现.因此,现在的目标是在Javascript 1.5(ECMA 4)中找到此迭代器函数的实现.
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通常会混淆this因为回调是call-ed(这就是为什么each在Prototype中接受第二个参数).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,因为迭代器可以迭代普通对象(参见JavaScript 1.7).
编辑3: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
JQuery有each()方法:http: //api.jquery.com/jQuery.each/
但即使在Moo或Dojo等其他库中也可能存在类似的东西.
Javascript 1.7实现了Iterator函数:https: //developer.mozilla.org/en/Core_JavaScript_1.5_Guide/Iterators_and_Generators
好吧,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,在这里和那里做出权衡,在决定这个时候我并没有想到很难:).
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)有趣的东西是在
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样一个类似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(' # 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>
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