Question

<select id="sel">
    <option id="1">aa</option>
    <option id="2">bb</option>
    <option id="3">cc</option>
</select>

<select id="two">
    <option id="1">aa</option>
    <option id="2">bb</option>
    <option id="3">cc</option>
</select>


function showalert(){
  alert($(this).find('option:selected').attr('id'));
}

$("#sel").change(function(){
   showalert();
});

$("#two").change(function(){
   showalert();
});

How to correctly use $(this) in these function? Now this is undefined.

Answer 1

pass $(this) to the function.

function showalert(that){
  alert(that.find('option:selected').attr('id'));
}

$("#sel").change(function(){
   showalert($(this));
});

$("#two").change(function(){
   showalert($(this));
});

---

Edited from the comments.

The comments are suggesting that you do not pass a jQuery object and infact it makes sense as it is just extra code and should be refactored into the method.

function showalert(that){
  alert($(that).find('option:selected').attr('id'));
}

$("#sel").change(function(){
   showalert(this);
});

$("#two").change(function(){
   showalert(this);
});