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    获取不到元素,获取值为null
    19
    0

    问题描述

    图片描述
    图片描述

    问题出现的环境背景及自己尝试过哪些方法

    报错元素为“null”,但是cname却能获取。报错是什么意思?
    尝试过吧引用的js文件都放到下面执行也不行

    相关代码

    前端页面

    <div class="modal-body">
                        <ul id="BranchType" class="nav nav-tabs">
                            <li class="active" id="applyMergeLi  ">
                                <a id="applyMergeA" href="#ApplyMerge" onclick=setCookieApplyMerge() data-toggle="tab">申请合入</a>
                            </li>
                            <li  id="applyPublishLi " class="active1" >
                                <a id="applyPublisA" href="#ApplyPublish" onclick=setCookieApplyPublish() data-toggle="tab">申请发布</a>
                                </li>
                            <li  id="mergeReviewLogLi" class="active2">
                                <a id="mergeReviewLogA" href="#MergeReviewLog" onclick=setCookieMergeReviewLog() data-toggle="tab">合入审批记录</a>
                            </li>
                            <li  id="publishReviewLogLi" class="active3" >
                                <a id="publishReviewLogA" href="#PublishReviewLog" onclick=setCookiePublishReviewLog() data-toggle="tab">发布审批记录</a>
                            </li>
                        </ul>
                        </div>
    <div 方法定义部分 common.js>
    function hasClass( elementOne,cName )
    {
        if (elementOne.className==null){
            return false;
        }
        return !!elementOne.className.match( new RegExp( "(\\s|^)" + cName + "(\\s|$)") ); // ( \\s|^ ) 判断前面是否有空格 (\\s | $ )判断后面是否有空格 两个感叹号为转换为布尔值 以方便做判断
    }
    
    function addClass( elementOne,cName )
    {
        if( !hasClass( elementOne,cName ) ){
            elementOne.className += " " + cName;
        };
    }
    
    function removeClass( elementOne,cName )
    {
        if( hasClass( elementOne,cName ) ){
            elementOne.className = elementOne.className.replace( new RegExp( "(\\s|^)" + cName + "(\\s|$)" )," " ); // replace方法是替换
        };
    }
    
    </div>
    
    <div  方法调用部分`请输入代码`>
    
    function onloadApplyPage()
    {
        var applyInfoPage = getCookie("applyInfoPage");
        var applyMergeLi = document.getElementById("applyMergeLi");
        var applyPublishLi = document.getElementById("applyPublishLi");
        var mergeReviewLogLi = document.getElementById("mergeReviewLogLi");
        var publishReviewLogLi = document.getElementById("publishReviewLogLi");
        var ApplyMerge = document.getElementById("ApplyMerge");
        var ApplyPublish = document.getElementById("ApplyPublish");
        var MergeReviewLog = document.getElementById("MergeReviewLog");
        var PublishReviewLog = document.getElementById("PublishReviewLog");
        if(applyInfoPage==1)
        {
            //为这个类移除属性
            addClass(applyMergeLi,"active");
            removeClass(applyPublishLi,"active");
            removeClass(mergeReviewLogLi,"active"); 
            removeClass(publishReviewLogLi,"active");         
            $("#applyMergeA").attr("aria-expanded","true");
            $("#applyPublishA").attr("aria-expanded","false");
            $("#mergeReviewLogA").attr("aria-expanded","false");
            $("#publishReviewLogA").attr("aria-expanded","false");
            addClass(ApplyMerge,"active");
            removeClass(ApplyPublish,"active");
            removeClass(MergeReviewLog,"active");
            removeClass(PublishReviewLog,"active");        
        }
        
        if(applyInfoPage==2)
        {
            //为这个类移除属性
            removeClass(applyMergeLi,"active");
            addClass(applyPublishLi,"active");
            removeClass(mergeReviewLogLi,"active"); 
            removeClass(publishReviewLogLi,"active");         
            $("#applyMergeA").attr("aria-expanded","false");
            $("#applyPublishA").attr("aria-expanded","true");
            $("#mergeReviewLogA").attr("aria-expanded","false");
            $("#publishReviewLogA").attr("aria-expanded","false");
            removeClass(ApplyMerge,"active");
            addClass(ApplyPublish,"active");
            removeClass(MergeReviewLog,"active");
            removeClass(PublishReviewLog,"active");         
        }
    
        if(applyInfoPage==3)
        {
            //为这个类移除属性
            removeClass(applyMergeLi,"active");
            removeClass(applyPublishLi,"active");
            addClass(mergeReviewLogLi,"active"); 
            removeClass(publishReviewLogLi,"active");         
            $("#applyMergeA").attr("aria-expanded","false");
            $("#applyPublishA").attr("aria-expanded","false");
            $("#mergeReviewLogA").attr("aria-expanded","true");
            $("#publishReviewLogA").attr("aria-expanded","false");
            removeClass(ApplyMerge,"active");
            removeClass(ApplyPublish,"active");
            addClass(MergeReviewLog,"active");
            removeClass(PublishReviewLog,"active");
            
        }
    
        if(applyInfoPage==4)
        {
            //为这个类移除属性
            removeClass(applyMergeLi,"active");
            removeClass(applyPublishLi,"active");
            removeClass(mergeReviewLogLi,"active"); 
            addClass(publishReviewLogLi,"active");         
            $("#applyMergeA").attr("aria-expanded","false");
            $("#applyPublishA").attr("aria-expanded","false");
            $("#mergeReviewLogA").attr("aria-expanded","false");
            $("#publishReviewLogA").attr("aria-expanded","true");
            removeClass(ApplyMerge,"active");
            removeClass(ApplyPublish,"active");
            removeClass(MergeReviewLog,"active");
            addClass(PublishReviewLog,"active");
            
        }
    }  
    
    
    </div>
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    • 只是個小人物 普通会员 1楼

      在JavaScript中,如果元素在DOM中不存在或者获取不到,那么尝试访问它的值就会返回null。例如:

      javascript var element = document.getElementById('myElement'); console.log(element.value); // undefined

      在这个例子中,我们尝试获取id为'myElement'的元素的值,但是这个元素在DOM中不存在,所以尝试访问它的值就会返回null。

      如果元素在DOM中存在,但是我们尝试访问它的值,那么它的值就会是undefined。例如:

      javascript var element = document.getElementById('myElement'); console.log(element.value); // undefined

      在这个例子中,我们尝试获取id为'myElement'的元素的值,但是这个元素在DOM中存在,但是我们尝试访问它的值就会返回undefined。

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