Question

我不知道为什么新生成的元素不能被下一个被调用的函数看到？感谢帮助！！解决方案：添加async：false以禁用异步功能，以确保在出生过程后执行test-output-2和test-output-3。默认情况下，ajax使用async：true，就像多线程一样。

function birth(mom)
{
    $.ajax(
    {url: "/cgi-bin/count.cgi",   // return 3 for sure
     async: false,   // add this to disable asynchronous feature to make sure test-output-2 and test-output-3 executed after birth process
     success: function(xkids)     // xkids is 3
     {
         for( var i = 0; i < xkids; i++ )
         {
             mom.appendChild(document.createElement("div"));
             mom.children[i].setAttribute("id", "child-"+i);
         }

         document.getElementById("test-output-1").innerHTML = mom.children.length;   // now there are 3 children
     }
    });
     document.getElementById("test-output-2").innerHTML = mom.children.length;   // there are 0 children if async: true

} 

var marry = document.getElementById("Marry"); // currently no child
birth(marry);

function whereIsTheChildren()
{
    document.getElementById("test-output-3").innerHTML = marry.children.length;   // there are 0 children if async: true
} 
whereIsTheChildren();

Answer 1

在加载之前尝试在DOM中找到一个元素是行不通的（脚本会在遇到它时立即运行。如果这个文件位于文件中的html之上，那么该元素将不会存在，因此不会被找到）

类似地，触发一个AJAX请求，然后表现为同步操作（等待操作在执行更多代码之前完成）将不起作用。

在第一个实例中，在浏览器有时间解析HTML之前遇到代码，因此当您尝试获取对它的引用时，DOM中不存在该元素 - 这可以通过等待来修复该文件表明它已完成装载。

第二个问题是在触发birth函数后立即触发whereIsTheChildren函数。不幸的是，ajax请求仍然悬而未决，所以我们还没有从中得到我们需要使用的结果。通过将调用whereIsTheChildren置于ajax请求的成功回调中来解决此问题。

我使用vanilla JS和PHP编写了一个快速示例 - 只需将请求替换为带有CGI的php文件。

<强> getKidCount.php

<?php
    echo "3";
?>

<强>的index.html

<!doctype html>
<html>
<head>
<script>
"use strict";
function byId(id,parent){return (parent == undefined ? document : parent).getElementById(id);}

function myAjaxGet(url, successCallback, errorCallback)
{
    var ajax = new XMLHttpRequest();
    ajax.onreadystatechange = function()
    {
        if (this.readyState==4 && this.status==200)
            successCallback(this);
    }
    ajax.onerror = function()
    {
        console.log("AJAX request failed to: " + url);
        errorCallback(this);
    }
    ajax.open("GET", url, true);
    ajax.send();
}

window.addEventListener('load', onDocLoaded, false);

function onDocLoaded(evt)
{
    //birth(3, byId("Marry") );
    myBirth( byId('Marry') );
}

function myBirth(parentElem)
{
    myAjaxGet('getKidCount.php', onAjaxSuccess, onAjaxFail);

    function onAjaxSuccess(ajax)
    {
        var numKids = parseInt(ajax.responseText);
        for (var i=0; i<numKids; i++)
        {
            var div = document.createElement('div');
            div.id = ("child-"+i);
            parentElem.appendChild(div);
        }
        document.getElementById("test-output-1").innerHTML = parentElem.children.length;   // now there are 3 children
        whereIsTheChildren();
    }
    function onAjaxFail(ajax)
    {
        alert("Ajax failed. :(");
    }
}

function whereIsTheChildren()
{
    document.getElementById("test-output-2").innerHTML = byId('Marry').children.length;   // there are 0 children
} 


/*
function birth(xkids, mom)
{
    for( var i = 0; i < xkids; i++ )
    {
        mom.appendChild(document.createElement("div"));
        mom.children[i].setAttribute("id", "child-"+i);
    }
    document.getElementById("test-output-1").innerHTML = mom.children.length;   // now there are 3 children
} 

function birth(mom)
{
    $.ajax(
    {url: "/cgi-bin/count.cgi",   // return 3 for sure
     success: function(xkids)     // xkids is 3
     {
         for( var i = 0; i < xkids; i++ )
         {
             mom.appendChild(document.createElement("div"));
             mom.children[i].setAttribute("id", "child-"+i);
         }

         document.getElementById("test-output-1").innerHTML = mom.children.length;   // now there are 3 children
     }
     document.getElementById("test-output-2").innerHTML = mom.children.length;   // now there are 0 children
} 
*/
</script>
</head>
<body>
    <div id='test-output-1'></div>
    <div id='test-output-2'></div>
    <div id='Marry'></div>
</body>
</html>

Answer 2

修改为在DOM中表示也在console.log中

＆＃13;

function birth(xkids, mom) {
  var mom = document.querySelector(mom);
  console.log('Mom: '+mom.id);
  for (var i = 0; i < xkids; i++) {
    mom.appendChild(document.createElement("div"));
    mom.children[i].setAttribute("id", "child-" + i);
    mom.children[i].innerHTML = mom.children[i].id;
  }
  console.log(mom.id+' has '+mom.children.length+' children');
  var test = document.createElement("output");
  document.body.appendChild(test);
  test.value = mom.id + ' ' + mom.children.length;
}

birth(3, '#Marry');
birth(5, '#Liz');
birth(2, '#Betty');

＆＃13;

div {
  outline: 1px solid black;
  width: 100px;
  height: 30px;
}
output {
  outline: 1px solid red;
  color: red;
  margin: 10px auto;
  padding: 2px;
  float: left;
}
.mom {
  outline: 1px dashed blue;
  width: 100px;
  height: auto;
  padding: 5px;
  display: inline-block;
}

＆＃13;

<div id="Marry" class="mom">Marry</div>
<div id="Liz" class="mom">Liz</div>
<div id="Betty" class="mom">Betty</div>

＆＃13;

Answer 3

你把它放在window.onload事件处理程序中吗？您的代码正常运行，请查看此fiddle

window.onload=function(){
function birth(xkids, mom)
{
    for( var i = 0; i < xkids; i++ )
    {
        mom.appendChild(document.createElement("div"));
        mom.children[i].setAttribute("id", "child-"+i);
    }

    document.getElementById("test-output-1").innerHTML = mom.children.length;   // now there are 3 children
} 

var marry = document.getElementById("Marry"); // currently no child
birth(3, marry);

function whereIsTheChildren()
{
    document.getElementById("test-output-2").innerHTML = marry.children.length;   // there are 0 children
} 
whereIsTheChildren();
}

Javascript无法看到动态生成的元素？

3 个答案: