如何获取 class 包含 2 个名称的 getelementbyClassname？

Question

我有一个 class 有两个名字 class=test-select r10 我有十行。例如：

var res = {};

var els;
for (var r = 1; r <= 10; r++) {
  els = document.getElementsByClassName("r" + r);
  console.log("Found " + els.length + " for r" + r);
  for (var i = 0; i < 4; i++) {
    els[i].selectedIndex = res["r" + r][i];
  }
}

<table>
  <tr class="info" id="alertr1">
    <td width="30px">1</td>
    <td width="200px">Likes Authority</td>
    <td width="75px;">
      <select class="test-select r1" name="qtyL" onchange="this.size=1" onmouseout="this.size=1" onmouseover="this.size=this.options.length" style="position: absolute; z-index:9999;">
        <option value="0">-</option>
        <option value="1">1</option>
        <option value="2">2</option>
        <option value="3">3</option>
        <option value="4">4</option>
      </select>
    </td>
    <td width="200px">Enthusiastic</td>
    <td width="75px;">
      <select class="test-select r1" name="qtyO" onchange="this.size=1" onmouseout="this.size=1" onmouseover="this.size=this.options.length" style="position: absolute; z-index:9999;">
        <option value="0">-</option>
        <option value="1">1</option>
        <option value="2">2</option>
        <option value="3">3</option>
        <option value="4">4</option>
      </select>
    </td>
  </tr>
</table>

如何使用 getelementByClassName 获取 class 的第二个名字？？

Answer 1

好的，我假设你的代码有一些不准确的地方：

你必须不同 select 在 json 中的相应数据，你不能假设数据在 json 中的顺序将始终对应于您 UI:

中元素的顺序

res = JSON.parse(localStorage.getItem("testingvalue"));

// res now should be in form of
// res = {
//   r1: {
//     qtyL: 2,
//     qtyO: 3,
//   },
//   r2: {
//      ...
//   },
//   ...
// };

你不应该将任何幻数硬编码到你的代码中，尤其是当它是关于json数据结构时：

var thunks = Object.keys(res).filter(function (name) {
  return name.match(/^r(\d+)$/);
});
console.log('found stat thunks:', thunks.join(', '));

for (var r = 0; r < thunks.length; r++) {
  var thunk = thunks[r];
  var stats = res[thunk];
  var els = document.querySelectorAll("." + thunk);
  console.log('supplied stats for "' + thunk + '" thunk:', JSON.stringify(stats));
  console.log('found "<select>" elements:', els.length);
  ...

您可能不应该假设您在 UI 中的元素将被命名为与持久化数据对象中的键完全相同：

// some ui-data bridge
function findSelectsByThunkName(name) {
    if (name.match(/^r\d+$/)) { // stats thunk
        return document.querySelectorAll("." + name);
    } elseif (...) {
       ...
    }

   return [];
}

...

var thunks = Object.keys(res).filter(function (name) {
  return name.match(/^r(\d+)$/);
});
console.log('found stat thunks:', thunks.join(', '));

for (var r = 0; r < thunks.length; r++) {
  var thunk = thunks[r];
  var stats = res[thunk];
  var els = findSelectsByThunkName(thunk);
  ...

工作片段：

// jQuery has 'shortcut' for '$(document).ready(function () { ... });'
// just use '$(function () { ... });' for simplicity's sake
$(function(){
  var res = null;

  try { 
    // assuming 'testingvalue' contains something like '{"r1":{"qtyL": 2,"qtyO": 3,...},"r2":{...},"something":[...],"and_other":1212,..}'
    res = {
      "r1": {
        "qtyL": 2,
        "qtyO": 3,
      },
      "r2": {
      },
      "something": [],
      "and_other":1212,
    }
    
    //res = JSON.parse(localStorage.getItem("testingvalue"));

    var thunks = 
      // get all keys from 'res' object (will get something like ["r1", "r2", "something", "and_other", ...])
      Object.keys(res)
      // and filter them to get only those...
      .filter(function (name) {
        return (
          name.match(
            // that starts (^ symbol) 
            // with "r" character
            // and then have any digit (\d sequence),
            // probably, even more than one (+ symbol)
            // and then ends ($ symbol)
            /^r(\d+)$/
            // this is called "regular expression"
            // you can read more about regexp's on supplied link [1]
          )
        );
      });
      
    // thunks variable now holds the list of "res" object keys, that are corresponding to "^r\d+$" pattern, like ["r1", "r2"]
    
    // as 'array' variables in javascript are in fact objects, they support some convenient methods for array elements manipulation (like mentioned '.filter()' method) etc
    
    // '.join()' is a method of 'array' objects, that concatenates stringified elements of the array, gluing them with provided glue-string, so ["r1", "r2", "r3"] becomes "r1, r2, r3" in this case
    console.log('found stat thunks:', thunks.join(', '));

    // and also 'array' objects have '.length' property that contains current array length
    // we can use it to iterate over all actual elements
    // of array, instead of hard-coding expected array length, which is somewhat ureliable
    for (var r = 0; r < thunks.length; r++) {
      var thunk = thunks[r]; // take key from list (remember, that array element indices are starting from 0)
      var stats = res[thunk]; // now we can access a stats list from 'res' object by picked key
      
      // now we can get the list of 'select' nodes on our page by their selectors
      // ".class-name" in selector below actually means
      // find all elements on page ('document'), that have "class-name" class ("class-name" is specified in their "class" atribute)
      // mentioned "class-name" should only "occur at least once" in 'class' attribute, strict match isn't required, so ".r1" selector will match both <select class="r1"> and <select class="some-other-class r1 and-other and-another"> the same
      // more you can read on the provided link [2]
      var els = document.querySelectorAll("." + thunk);
      
      // btw, beware that '.querySelectorAll()' returns 'NodeList' object, not the 'Array'. It also have '.length' property (like regular arrays) and it's elements can be accessed via bracket-index array access syntax ('els[index]'), but it doesn't have the same convenience mathods, as regular array objects (so, you can't, for example, filter it with 'els.filter()')

      // print data to developer console for debugging
console.log('supplied stats for "' + thunk + '" thunk:', JSON.stringify(stats));
      console.log('found "<select>" elements:', els.length);
      
      // iterate over found 'select' elements
      for (var i = 0; i < els.length; i++) {
        var select = els[i];
        
        // '.getAttribute(attributeName)' returns value of any attribute of html node,
        // for example, for html, supplied in the example, it will return "qtyL" and "qtyO" as "name" attributes for provided 'select' html nodes 
        var name = select.getAttribute("name");
        
        // we can use that "name" as key to access stat indexes from "res" object without relying, that stats in that object are listed and persisted in the same order, in which we are placing our 'select' elements in the page html code, and in which they were fetched and returned by '.querySelectorAll()' method.
        select.selectedIndex = +stats[name];
      }
    }
  } catch (error){
    console.log(error.message);
  }
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<table>
  <tr class="info" id="alertr1">
    <td width="30px">1</td>
    <td width="200px">Likes Authority</td>
    <td width="75px;">
        <select class="test-select r1" style="position: absolute; z-index:9999;" onmouseover="this.size=this.options.length" onmouseout="this.size=1" onchange="this.size=1" name="qtyL">
            <option value="0">-</option>
            <option value="1">1</option>
            <option value="2">2</option>
            <option value="3">3</option>
            <option value="4">4</option>
        </select>
    </td>
    <td width="200px">Enthusiastic</td>
    <td width="75px;">
        <select class="test-select r1" style="position: absolute; z-index:9999;" onmouseover="this.size=this.options.length" onmouseout="this.size=1" onchange="this.size=1" name="qtyO">
            <option value="0">-</option>
            <option value="1">1</option>
            <option value="2">2</option>
            <option value="3">3</option>
            <option value="4">4</option>
        </select>
    </td>
  </tr>
</table>

有用的链接：

如何获取 class 包含 2 个名称的 getelementbyClassname？

How do I get getelementbyClassname which the class contain 2 name?

javascript

getelementsbyclassname