blocks|key|803249|text|Felix+Kling在问题的评论部分提供了以下正确答案|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|803250|if+(!$.trim(data)){+++
++++alert("What+follows+is+blank:+"+%2B+data);
}
else{+++
++++alert("What+follows+is+not+blank:+"+%2B+data);
}|code-block|syntax|javascript|803251|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/users/218196/felix-kling^0|0|B|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

<p>The following correct answer was provided in the comment section of the question by <a href="https://stackoverflow.com/users/218196/felix-kling">Felix Kling</a>:</p>

<pre><code>if (!$.trim(data)){   
    alert("What follows is blank: " + data);
}
else{   
    alert("What follows is not blank: " + data);
}
</code></pre>


blocks|key|803224|text|//if(data="undefined"){|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|803225|这是一个赋值语句，而不是比较。另外，"undefined"是一个字符串，它是一个属性。检查它如下所示：if+(data+===+undefined)+(没有引号，否则是一个字符串值)|unstyled|offset|length|style|CODE|803226|如果未定义它，则可能返回一个空字符串。您也可以尝试检查类似于falsy的if+(!data)值。|803227|entityMap^0|0|I|B|1F|N|0|U|5|10|A|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|P|8|@$G|Q|H|R|I|J]|$G|S|H|T|I|J]]|9|@]|A|$]]|$1|K|3|L|5|F|7|U|8|@$G|V|H|W|I|J]|$G|X|H|Y|I|J]]|9|@]|A|$]]|$1|M|3|-4|5|F|7|Z|8|@]|9|@]|A|$]]]|N|$]]

<pre><code>//if(data="undefined"){
</code></pre>

<p>This is an assignment statement, not a comparison. Also, <code>"undefined"</code> is a string, it's a property. Checking it is like this: <code>if (data === undefined)</code> (no quotes, otherwise it's a string value)</p>

<p>If it's not defined, you may be returning an empty string. You could try checking for a <code>falsy</code> value like <code>if (!data)</code> as well</p>


blocks|key|803288|text|if(data.trim()==''){alert("Nothing+Found");}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|803289|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>if(data.trim()==''){alert("Nothing Found");}
</code></pre>


blocks|key|1502393|text|这对我来说很有效..。page.php上的PHP代码|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1502394|+$query_de="sql+statements+here";
+$sql_de+=+sqlsrv_query($conn,$query_de);
++++++if+($sql_de)
++++++{
++++++++echo+"SQLSuccess";
+++++++}
+++++++++exit();|code-block|syntax|javascript|1502395|然后AJAX代码会发出低语|1502396|jQuery.ajax({
++++++++++++++++++++url++:+"page.php",
++++++++++++++++++++type+:+"POST",
++++++++++++++++++++data+:+{
++++++++++++++++++++++++++++buttonsave+++:+1,
++++++++++++++++++++++++++++var1+++++++++:+val1,
++++++++++++++++++++++++++++var2+++++++++:+val2,
++++++++++++++++++++++++++++++},
++++++++++++++++++success:function(data)
+++++++++++++++++++++++++++{
+++++++++++++++++++++if(jQuery.trim(data)+===+"SQLSuccess")
+++++++++++++++++++++++++++++++++++{
+++++++++++++++++++++++++++alert("Se+agrego+correctamente");
++++++++++++++++++++++++++//+alert(data);
++++++++++++++++++++++++++++++++++++++}+else+{+alert(data);}
++++++++++++++++++++++++++++++},
+++++++++++++++++++error:+function(error)
+++++++++++++++++++++++++++{
++++++++++++++++++++alert("Error+AJAX+not+working:+"%2B+error+);
++++++++++++++++++++++++++++++}+
+++++++++++++++});+|1502397|注意：“SQLSuccess”一词必须来自PHP|1502398|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

<p>This worked form me.. 
PHP Code on page.php</p>

<pre><code> $query_de="sql statements here";
 $sql_de = sqlsrv_query($conn,$query_de);
      if ($sql_de)
      {
        echo "SQLSuccess";
       }
         exit();
</code></pre>

<p>and then AJAX Code has bellow</p>

<pre><code>jQuery.ajax({
                    url  : "page.php",
                    type : "POST",
                    data : {
                            buttonsave   : 1,
                            var1         : val1,
                            var2         : val2,
                              },
                  success:function(data)
                           {
                     if(jQuery.trim(data) === "SQLSuccess")
                                   {
                           alert("Se agrego correctamente");
                          // alert(data);
                                      } else { alert(data);}
                              },
                   error: function(error)
                           {
                    alert("Error AJAX not working: "+ error );
                              } 
               }); 
</code></pre>

<p>NOTE: the word 'SQLSuccess' must be received from PHP</p>


blocks|key|1502410|text|$.ajax({
++++type:"POST",
++++url:+"<?php+echo+admin_url('admin-ajax.php');+?>",
++++data:+associated_buildsorprojects_form,
++++success:function(data){
++++++++//+do+console.log(data);
++++++++console.log(data);
++++++++//+you'll+find+that+what+exactly+inside+data+
++++++++//+I+do+not+prefer+alter(data);+now+because,+it+does+not+
++++++++//+completes+requirement+all+the+time+
++++++++//+After+that+you+can+easily+put+if+condition+that+you+do+not+want+like
++++++++//+if(data+!=+'')
++++++++//+if(data+==+null)
++++++++//+or+whatever+you+want+
++++},
++++error:+function(errorThrown){
++++++++alert(errorThrown);
++++++++alert("There+is+an+error+with+AJAX!");
++++}+++++++++++++++
});|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1502411|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>$.ajax({
    type:"POST",
    url: "&lt;?php echo admin_url('admin-ajax.php'); ?&gt;",
    data: associated_buildsorprojects_form,
    success:function(data){
        // do console.log(data);
        console.log(data);
        // you'll find that what exactly inside data 
        // I do not prefer alter(data); now because, it does not 
        // completes requirement all the time 
        // After that you can easily put if condition that you do not want like
        // if(data != '')
        // if(data == null)
        // or whatever you want 
    },
    error: function(errorThrown){
        alert(errorThrown);
        alert("There is an error with AJAX!");
    }               
});
</code></pre>


<h2>What I have:</h2>

<p>I have jQuery AJAX function that returns HTML after querying a database. Depending on the result of the query, the function will either return HTML code or nothing (i.e. blank) as desired.</p>

<h2>What I need:</h2>

<p>I need to conditionally check for when the data is blank.</p>

<h2>My code:</h2>

<pre><code>$.ajax({
    type:"POST",
    url: "&lt;?php echo admin_url('admin-ajax.php'); ?&gt;",
    data: associated_buildsorprojects_form,
    success:function(data){
        if(!data){  
        //if(data="undefined"){
        //if(data==="undefined"){
        //if(data==null){
        //if(data.length == 0){
        //if ( data.length != 0 ){
        //if(data===0){
        //if(data==="0"){   
            alert("Data: " + data);
        }
    },
    error: function(errorThrown){
        alert(errorThrown);
        alert("There is an error with AJAX!");
    }               
});
</code></pre>

<h2>My problem:</h2>

<p>I've tried a variety of conditions but none correctly check the data. Based on my findings, a blank alert message does not mean data is </p>

<ol>
<li>empty</li>
<li>non-existent</li>
<li>equal to zero</li>
<li>of length zero</li>
<li>null</li>
<li>undefined</li>
</ol>

<p>If it's none of these things, how can I therefore conditionally check for the data that yields a blank alert message?</p>


Check if AJAX response data is empty/blank/null/undefined/0

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我所拥有的：我有jQuery AJAX函数，在查询数据库后返回HTML。根据查询的结果，函数将返回HTML代码或不返回(即空白)所需的任何内容。我需要的是：当数据为空白时，我需要有条件地检查。我的代码：$.ajax({    type:"POST",    url: "<?php echo admin_url('admin-ajax.php'); ?>",    data: associated_

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