Send text-box id to function in JavaScript?

Question

I tried to get the text-box's id via its event function but it seems $a doesn't work because the system understands this as text, what should I do?

<select class="btn btn-outline-secondary dropdown-toggle"
        type="button"
        class="dropdown-menu" 
        onchange="validateSelectBox(this,'skill_input4')">

<select class="btn btn-outline-secondary dropdown-toggle"
        type="button"
        class="dropdown-menu" 
        onchange="validateSelectBox1(this,'skill_input3')">

function validateSelectBox(obj, $a){
  
    var options = obj.children;
 
    var html = '';
 
    for (var i = 0; i < options.length; i++){
        if (options[i].selected){
            html += options[i].value;
        }
    }
    // this is the error, the textbox does not change data
    // when I select the combobox
    document.getElementById('$a').value = html; 
}

Answer 1

你不需要把它放在引号中，因为它是一个变量，你能试试这个吗

document.getElementById($a).value = html; 

Answer 2

  function validateSelectBox(obj, a)
{
  
    var options = obj.children;
 
    var html = '';
 
  
    for (var i = 0; i < options.length; i++){
        if (options[i].selected){
            html += options[i].value;
        }
    }
document.getElementById(a).value = html; 
}

Answer 3

如果skill_input3 和skill_input4 是提到的文本框的id，你应该调用document.getElementById($a).value=html

Answer 4

 function validateSelectBox(obj,$a)
{
  
    var options = obj.children;
 
    var html = '';
 
  
    for (var i = 0; i < options.length; i++){
        if (options[i].selected){
            html += options[i].value;
        }
    }
document.getElementById($a).value = html;//remove '$a' from quotes.
}

Remove'$a' From Quotes

Answer 5

You have to remove $a from quotes as it a variable

function validateSelectBox(obj,$a)
{
  
    var options = obj.children;
 
    var html = '';
 
  
    for (var i = 0; i < options.length; i++){
        if (options[i].selected){
            html += options[i].value;
        }
    }
document.getElementById($a).value = html;//remove '$a' from quotes.
}