Question

我如何从元素中读取索引？例如：

我有代码：

<div class="a">
<span id="el">Yeah!</span>
<span class="span">1</span>
<span class="span">2MANO</span>
</div>

和javascript： var mySpan = document.getElementsByTagName("span")[0]; // it span id="el"没关系，

但我怎么能从这个元素的这个跨度索引中读取

var span= document.getElementById("el"); // i should get index 0 but i cant do that

Answer 1

你说你的意思是它在父母中的位置：为此，计算previousSibling或previousElementSibling的次数（取决于你是想要计算其他类型的节点还是只计算元素）不是null：

计算所有节点类型：

function getIndex(node) {
  var index = 0;
  while (node.previousSibling) {
    node = node.previousSibling;
    ++index;
  }
  return index;
}
console.log(getIndex(document.getElementById("el")));  // 0
console.log(getIndex(document.getElementById("el2"))); // 5, counts text nodes

<div class="a">
<span id="el">Yeah!</span>
<span class="span">1</span>
<span class="span" id="el2">2MANO</span>
</div>

仅计算元素：

function getElementIndex(node) {
  var index = 0;
  while (node.previousElementSibling) {
    node = node.previousElementSibling;
    ++index;
  }
  return index;
}
console.log(getElementIndex(document.getElementById("el")));  // 0
console.log(getElementIndex(document.getElementById("el2"))); // 2, counts only elements

<div class="a">
<span id="el">Yeah!</span>
<span class="span">1</span>
<span class="span" id="el2">2MANO</span>
</div>

Answer 2

如果您按getElementById获取元素，则无法进行。您需要引用父项并通过父项子项获取它的索引：

var nodes = Array.prototype.slice.call( document.getElementsByClassName('a')[0].children );
var span = document.getElementById('el');
var index = nodes.indexOf(span);
console.log(index); // 0
var span = document.getElementById('el2');
var index = nodes.indexOf(span);
console.log(index); // 1

<div class="a">
<span id="el">Yeah!</span>
<span id="el2">Yeah!</span>
</div>

Answer 3

您可以查看父节点及其子节点（使用ES6语法）：

const span = document.getElementById("el");
const idx = [...span.parentNode.children].findIndex(n => n === span);

以下是ES5的替代方案：

idx = Array.prototype.slice.call(span.parentNode.children)
  .reduce(function(result, node, i) {
    return node === span ? i : result;
  }, -1);

如何获取索引元素？

3 个答案: