我在此javascript计算中做错了什么？

Question

I have two inputs that can hold a value and where a value is typed in.
calculate() kinda do the job but I getting an error in the console :
Uncaught TypeError: Cannot set property 'value' of null(…)
But for calculate() I get only that error!

    if($sal>10){
         echo '<td>
         <input type="text" oninput="calculate()"  name="monthly_sum_019" id="monthly_sum_019" value="">
         <input type="hidden" class="input toggle all" id="monthly_sum_019" oninput="calculate()" value="" placeholder="'.$sal.'"></td>';       
    }else{
         echo '<td>
         <input type="text" oninput="calculate()"  name="monthly_sum_019" id=""  value="">
         <input type="hidden" class="input toggle all" id="monthly_sum_019" oninput="calculatez()"  value="'.$sal.'"></td>';
        }

And have 2 inputs that returns result of calculation:

if($sal>10){
     echo '<td>
     <input type="text" id="result" name="reward_019"  value=""></td>'; 
}else{
     echo '<td>
     <input type="text" id="result2"  name="reward_019"  value=""></td>';           
    }

And the javascript:

<script>
    function calculate() {
        var myBox1 = parseFloat(document.getElementById('monthly_sum_019').value);  
        var myBox2 = parseFloat(document.getElementById('norm').value);
        var myBox3 = parseFloat(document.getElementById('time_hours_019').value);
        var result = document.getElementById('result'); 
        var myResult = (myBox1 / myBox2) * myBox3;

    result.value = myResult.toFixed(2);
    }   
</script>
<script>
    function calculatez() {
        var myBox1 = parseFloat(document.getElementById('hourmoney').value);    
        var myBox3 = parseFloat(document.getElementById('time_hours_019').value);
        var result2 = document.getElementById('result2');   
        var myResult = myBox3 * myBox1;
            result2.value = myResult.toFixed(2);                
    }
</script>

What is wrong?

Answer 1

Usually Cant do something of NULL means you try to select element but it's not presented in DOM.

I see that you try to select element with ID result2 but in your provided code I see that when $sal > 10 == true you do not put element with such ID.

Since it's PHP code you can have same ID in both if and else parts (but not in same part multiple times).