获取子节点索引

问题描述 投票：92回答：9

在直接的javascript（即，没有诸如jQuery之类的扩展等）中，有没有办法在其父节点内确定子节点的索引而不迭代并比较所有子节点？

EG，

var child = document.getElementById('my_element');
var parent = child.parentNode;
var childNodes = parent.childNodes;
var count = childNodes.length;
var child_index;
for (var i = 0; i < count; ++i) {
  if (child === childNodes[i]) {
    child_index = i;
    break;
  }
}

有没有更好的方法来确定孩子的指数？

javascript dom
9个回答
106
投票

你可以使用previousSibling属性迭代回到兄弟姐妹，直到你回到null并计算你遇到了多少兄弟姐妹：

var i = 0;
while( (child = child.previousSibling) != null ) 
  i++;
//at the end i will contain the index.

请注意，在像Java这样的语言中，有一个getPreviousSibling()函数，但是在JS中它已成为属性 - previousSibling。

104
投票

我喜欢使用indexOf。因为indexOf在Array.prototype而parent.children是NodeList，你必须使用call();这有点难看，但它是一个单行，并使用任何javascript dev应该熟悉的函数无论如何。

var child = document.getElementById('my_element');
var parent = child.parentNode;
// The equivalent of parent.children.indexOf(child)
var index = Array.prototype.indexOf.call(parent.children, child);
64
投票

ES6:

Array.from(element.parentNode.children).indexOf(element)

Explanation :

  • element.parentNode.children→返回element的兄弟，包括那个元素。
  • Array.from→将children的构造函数转换为Array对象
  • indexOf→你可以申请indexOf，因为你现在有一个Array对象。
33
投票

ES-短

[...element.parentNode.children].indexOf(element);

传播运算符是它的捷径

8
投票

添加（前缀为安全性）element.getParentIndex（）：

Element.prototype.PREFIXgetParentIndex = function() {
  return Array.prototype.indexOf.call(this.parentNode.children, this);
}
5
投票

我假设给定一个元素，其中所有子元素按顺序排列在文档上，最快的方法应该是进行二元搜索，比较元素的文档位置。但是，正如结论中所介绍的那样，假设被拒绝了。您拥有的元素越多，性能潜力就越大。例如，如果您有256个元素，那么（最佳）您只需要检查其中的16个元素！对于65536，只有256！性能增长到2的力量！查看更多数字/统计数据。访问Wikipedia

(function(constructor){
   'use strict';
    Object.defineProperty(constructor.prototype, 'parentIndex', {
      get: function() {
        var searchParent = this.parentElement;
        if (!searchParent) return -1;
        var searchArray = searchParent.children,
            thisOffset = this.offsetTop,
            stop = searchArray.length,
            p = 0,
            delta = 0;

        while (searchArray[p] !== this) {
            if (searchArray[p] > this)
                stop = p + 1, p -= delta;
            delta = (stop - p) >>> 1;
            p += delta;
        }

        return p;
      }
    });
})(window.Element || Node);

然后，您使用它的方式是获取任何元素的'parentIndex'属性。例如，查看以下演示。

(function(constructor){
   'use strict';
    Object.defineProperty(constructor.prototype, 'parentIndex', {
      get: function() {
        var searchParent = this.parentNode;
        if (searchParent === null) return -1;
        var childElements = searchParent.children,
            lo = -1, mi, hi = childElements.length;
        while (1 + lo !== hi) {
            mi = (hi + lo) >> 1;
            if (!(this.compareDocumentPosition(childElements[mi]) & 0x2)) {
                hi = mi;
                continue;
            }
            lo = mi;
        }
        return childElements[hi] === this ? hi : -1;
      }
    });
})(window.Element || Node);

output.textContent = document.body.parentIndex;
output2.textContent = document.documentElement.parentIndex;
Body parentIndex is <b id="output"></b><br />
documentElements parentIndex is <b id="output2"></b>

限制

  • 该解决方案的实现在IE8及以下版本中不起作用。

Binary VS Linear Search On 200 thousand elements (might crash some mobile browsers, BEWARE!):

  • 在这个测试中，我们将看到线性搜索找到中间元素VS二进制搜索需要多长时间。为什么中间元素？因为它位于所有其他位置的平均位置，所以它最好代表所有可能的位置。

Binary Search

(function(constructor){
   'use strict';
    Object.defineProperty(constructor.prototype, 'parentIndexBinarySearch', {
      get: function() {
        var searchParent = this.parentNode;
        if (searchParent === null) return -1;
        var childElements = searchParent.children,
            lo = -1, mi, hi = childElements.length;
        while (1 + lo !== hi) {
            mi = (hi + lo) >> 1;
            if (!(this.compareDocumentPosition(childElements[mi]) & 0x2)) {
                hi = mi;
                continue;
            }
            lo = mi;
        }
        return childElements[hi] === this ? hi : -1;
      }
    });
})(window.Element || Node);
test.innerHTML = '<div> </div> '.repeat(200e+3);
// give it some time to think:
requestAnimationFrame(function(){
  var child=test.children.item(99.9e+3);
  var start=performance.now(), end=Math.round(Math.random());
  for (var i=200 + end; i-- !== end; )
    console.assert( test.children.item(
        Math.round(99.9e+3+i+Math.random())).parentIndexBinarySearch );
  var end=performance.now();
  setTimeout(function(){
    output.textContent = 'It took the binary search ' + ((end-start)*10).toFixed(2) + 'ms to find the 999 thousandth to 101 thousandth children in an element with 200 thousand children.';
    test.remove();
    test = null; // free up reference
  }, 125);
}, 125);
<output id=output> </output><br />
<div id=test style=visibility:hidden;white-space:pre></div>

Backwards (`lastIndexOf`) Linear Search

(function(t){"use strict";var e=Array.prototype.lastIndexOf;Object.defineProperty(t.prototype,"parentIndexLinearSearch",{get:function(){return e.call(t,this)}})})(window.Element||Node);
test.innerHTML = '<div> </div> '.repeat(200e+3);
// give it some time to think:
requestAnimationFrame(function(){
  var child=test.children.item(99e+3);
  var start=performance.now(), end=Math.round(Math.random());
  for (var i=2000 + end; i-- !== end; )
    console.assert( test.children.item(
        Math.round(99e+3+i+Math.random())).parentIndexLinearSearch );
  var end=performance.now();
  setTimeout(function(){
    output.textContent = 'It took the backwards linear search ' + (end-start).toFixed(2) + 'ms to find the 999 thousandth to 101 thousandth children in an element with 200 thousand children.';
    test.remove();
    test = null; // free up reference
  }, 125);
});
<output id=output> </output><br />
<div id=test style=visibility:hidden;white-space:pre></div>

Forwards (`indexOf`) Linear Search

(function(t){"use strict";var e=Array.prototype.indexOf;Object.defineProperty(t.prototype,"parentIndexLinearSearch",{get:function(){return e.call(t,this)}})})(window.Element||Node);
test.innerHTML = '<div> </div> '.repeat(200e+3);
// give it some time to think:
requestAnimationFrame(function(){
  var child=test.children.item(99e+3);
  var start=performance.now(), end=Math.round(Math.random());
  for (var i=2000 + end; i-- !== end; )
    console.assert( test.children.item(
        Math.round(99e+3+i+Math.random())).parentIndexLinearSearch );
  var end=performance.now();
  setTimeout(function(){
    output.textContent = 'It took the forwards linear search ' + (end-start).toFixed(2) + 'ms to find the 999 thousandth to 101 thousandth children in an element with 200 thousand children.';
    test.remove();
    test = null; // free up reference
  }, 125);
});
<output id=output> </output><br />
<div id=test style=visibility:hidden;white-space:pre></div>

PreviousElementSibling Counter Search

计算PreviousElementSiblings的数量以获取parentIndex。

(function(constructor){
   'use strict';
    Object.defineProperty(constructor.prototype, 'parentIndexSiblingSearch', {
      get: function() {
        var i = 0, cur = this;
        do {
            cur = cur.previousElementSibling;
            ++i;
        } while (cur !== null)
        return i; //Returns 3
      }
    });
})(window.Element || Node);
test.innerHTML = '<div> </div> '.repeat(200e+3);
// give it some time to think:
requestAnimationFrame(function(){
  var child=test.children.item(99.95e+3);
  var start=performance.now(), end=Math.round(Math.random());
  for (var i=100 + end; i-- !== end; )
    console.assert( test.children.item(
        Math.round(99.95e+3+i+Math.random())).parentIndexSiblingSearch );
  var end=performance.now();
  setTimeout(function(){
    output.textContent = 'It took the PreviousElementSibling search ' + ((end-start)*20).toFixed(2) + 'ms to find the 999 thousandth to 101 thousandth children in an element with 200 thousand children.';
    test.remove();
    test = null; // free up reference
  }, 125);
});
<output id=output> </output><br />
<div id=test style=visibility:hidden;white-space:pre></div>

No Search

对于基准测试，如果浏览器优化了搜索，测试结果将是什么。

test.innerHTML = '<div> </div> '.repeat(200e+3);
// give it some time to think:
requestAnimationFrame(function(){
  var start=performance.now(), end=Math.round(Math.random());
  for (var i=2000 + end; i-- !== end; )
    console.assert( true );
  var end=performance.now();
  setTimeout(function(){
    output.textContent = 'It took the no search ' + (end-start).toFixed(2) + 'ms to find the 999 thousandth to 101 thousandth children in an element with 200 thousand children.';
    test.remove();
    test = null; // free up reference
  }, 125);
});
<output id=output> </output><br />
<div id=test style=visibility:hidden></div>

结论

但是，在Chrome中查看结果后，结果与预期相反。数字转发线性搜索是一个令人惊讶的187毫秒，3850％，比二进制搜索更快。显然，Chrome以某种方式神奇地超越了console.assert并对其进行了优化，或者（更乐观地）Chrome内部使用了数字索引系统用于DOM，并且当在Array.prototype.indexOf对象上使用时，这个内部索引系统通过应用于HTMLCollection的优化来暴露。

3
投票

当节点具有大量兄弟节点时，使用binary search algorithm来提高性能。

function getChildrenIndex(ele){
    //IE use Element.sourceIndex
    if(ele.sourceIndex){
        var eles = ele.parentNode.children;
        var low = 0, high = eles.length-1, mid = 0;
        var esi = ele.sourceIndex, nsi;
        //use binary search algorithm
        while (low <= high) {
            mid = (low + high) >> 1;
            nsi = eles[mid].sourceIndex;
            if (nsi > esi) {
                high = mid - 1;
            } else if (nsi < esi) {
                low = mid + 1;
            } else {
                return mid;
            }
        }
    }
    //other browsers
    var i=0;
    while(ele = ele.previousElementSibling){
        i++;
    }
    return i;
}
0
投票
Object.defineProperties(Element.prototype,{
group : {
    value: function (str, context) {
        // str is valid css selector like :not([attr_name]) or .class_name
        var t = "to_select_siblings___";
        var parent = context ? context : this.parentNode;
        parent.setAttribute(t, '');
        var rez = document.querySelectorAll("[" + t + "] " + (context ? '' : ">") + this.nodeName + (str || "")).toArray();
        parent.removeAttribute(t);            
        return rez;  
    }
},
siblings: {
    value: function (str, context) {
        var rez=this.group(str,context);
        rez.splice(rez.indexOf(this), 1);
        return rez; 
    }
},
nth: {  
    value: function(str,context){
       return this.group(str,context).indexOf(this);
    }
}
}

防爆

/* html */
<ul id="the_ul">   <li></li> ....<li><li>....<li></li>   </ul>

 /*js*/
 the_ul.addEventListener("click",
    function(ev){
       var foo=ev.target;
       foo.setAttribute("active",true);
       foo.siblings().map(function(elm){elm.removeAttribute("active")});
       alert("a click on li" + foo.nth());
     });
-2
投票
<body>
    <section>
        <section onclick="childIndex(this)">child a</section>
        <section onclick="childIndex(this)">child b</section>
        <section onclick="childIndex(this)">child c</section>
    </section>

    <script src="//code.jquery.com/jquery-1.11.3.min.js"></script>
    <script>
        function childIndex(e){
            var i = 0;
            debugger
            while (e.parentNode.children[i] != e) i++;
            alert('child index '+i);
        }
    </script>
</body>
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