由于 javascript 获取 PHP 值，代码无法正常运行，我不知道如何比较它们

Question

<div class="content">
            <h1>Üdvözöllek, <?php echo $nickname; ?>! </h2>
            <h4>Válasszon hetet: </h4>

            <select class="select-selected" id="1" name="het" onchange="checkclass()">
                <option disabled selected value>Hét</option>
                <option value="1"><?php echo $sd->format('m.d')," - ", $ed->format('m.d');?></option>
                <option value="2"><?php echo $sd2->format('m.d')," - ", $ed2->format('m.d');?></option>
                <option value="3"><?php echo $sd3->format('m.d')," - ", $ed3->format('m.d');?></option>
            </select>

        </div >
        <div>

            <a id="class">
                <select class="select-selected" id="2" onchange="checksubject()" name="osztaly">
                <option disabled selected value><?php echo $class; ?></option></select>
            </a>
            <a id="subject">
                <select class="select-selected" id="3" name="tantargy">
                <option disabled selected value><?php echo $subject; ?></option></select>
            </a>
            <a id="bontotte"></a>
            <a id="classtwo"></a>
        </div>

        <script>
    function checkclass() {
        var het = document.getElementById('1').value;
        if(1<=het){
            var onosztaly = 
            '<select class="select-selected" name="osztaly">'+
            '<option disabled selected value><?php echo $class; ?>'+
            '<option value="<?php echo $class1; ?>"><?php echo $class1; ?></option>'+
            '<option value="<?php echo $class2; ?>"><?php echo $class2; ?></option>'+
            '<option value="<?php echo $class3; ?>"><?php echo $class3; ?></option>'+
            '<option value="<?php echo $class4; ?>"><?php echo $class4; ?></option>'+
            '<option value="<?php echo $class5; ?>"><?php echo $class5; ?></option>'+
            '<option value="<?php echo $class6; ?>"><?php echo $class6; ?></option>'+
            '<option value="<?php echo $class7; ?>"><?php echo $class7; ?></option>'+
            '</select>';        
            document.getElementById("class").innerHTML =(onosztaly);
        }
        }
    function checksubject() {
        var sub = document.getElementById('2').value;
        var clas = document.getElementById('2').value;
        if(sub == clas){
            var onsub = '<select class="select-selected" id="2" name="tantargy">'+
            '<option disabled selected value><?php echo $subject; ?></option>'+
            '<option value="<?php echo $subject1; ?>"><?php echo $subject1; ?></option>'+
            '<option value="<?php echo $subject2; ?>"><?php echo $subject2; ?></option>'+
            '<option value="<?php echo $subject3; ?>"><?php echo $subject3; ?></option>'+
            '<option value="<?php echo $subject4; ?>"><?php echo $subject4; ?></option>'+
            '</select>';
            document.getElementById("subject").innerHTML =(onsub);
        }
        }

    </script>

So the last one doesn't make it's select box to fill in, like the other one named "osztaly". I think i have a problem with the IF tag in the javascript because the values can't compare :)

Answer 1

You have overwritten your own select box via javascript

Change this code

 var onosztaly = 
   '<select class="select-selected" name="osztaly">'+

To

 var onosztaly = 
   '<select class="select-selected" id="2" onchange="checksubject()" name="osztaly">'+

it will work, means both the ID of the select box and the change event is lost when date is changed

to be frank your design is not good, there are effective methods to add options and remove options, innerHTML is very old style

the question text shows -- javascript getting PHP values -- this understanding is wrong

your entire code rendered as running HTML and given to browser, there is no more PHP in browser, only browser coding you are doing for drop down change

so when you think that are actually reading values from PHP, that is not a correct understanding

you are directly reading HTML components value only in javascript

Answer 2

As Dickens got the right way to make the code work, here is an example of correct output. Essentially source has some minor errors, which were eliminated here

 function checkclass() { var het = document.getElementById('1').value; if(1<=het){ var onosztaly = '<select class="select-selected" id="2" onchange="checksubject()" name="osztaly">'+ '<option disabled selected value>class</option>'+ '<option value="class1">class1</option>'+ '<option value="class2">class2</option>'+ '<option value="class3">class3</option>'+ '<option value="class4">class4</option>'+ '<option value="class5">class5</option>'+ '<option value="class6">class6</option>'+ '<option value="class7">class7</option>'+ '</select>'; document.getElementById("class").innerHTML =(onosztaly); } } function checksubject() { var onsub = '<select class="select-selected" name="tantargy">'+ '<option disabled selected value>subject</option>'+ '<option value="subject1">subject1</option>'+ '<option value="subject2">subject2</option>'+ '<option value="subject3">subject3</option>'+ '<option value="subject4">subject4</option>'+ '</select>'; document.getElementById("subject").innerHTML =(onsub); }

 <div class="content"> <h1>Üdvözöllek, nickname! </h2> <h4>Válasszon hetet: </h4> <select class="select-selected" id="1" name="het" onchange="checkclass()"> <option disabled selected value>Hét</option> <option value="1">date1</option> <option value="2">Date2</option> <option value="3">Date3</option> </select> </div > <div> <a id="class"> <select class="select-selected" id="2" onchange="checksubject()" name="osztaly"> <option disabled selected value>Class</option></select> </a> <a id="subject"> <select class="select-selected" id="3" name="tantargy"> <option disabled selected value>Subject</option></select> </a> <a id="bontotte"></a> <a id="classtwo"></a> </div>