Question

Update input field event onchange?

$A = array(A,B,C,D);

<select name="A" id="A" onchange="change_val()">
<?php 
foreach($A as $key=>$val){?>
    <option value="<?php echo $key?><?php echo $val?"></option>
<?php }?>
 </select>
<input name="seleted_value" id="seleted_value" value="Hello first time" >

I want to write a onchange method change_val() that do this task:

if select A ( by default ) show value ‘Hello first time’ into input field seleted_value

else show value have selected into input field seleted_value AND Disable this input field for read only.

Anybody could guide me how to do this?

  if selected= A =>show 'Hello first time'
  if selected= B =>show 'B'
  if selected= C =>show 'C'
  if selected= D =>show 'D'

Answer 1

Sure:

function change_val() { 
   var sel = document.getElementById('A'),
       lbl = document.getElementById('selected_value');

   lbl.disabled = (sel.selectedIndex !== 0);

   if(sel.selectedIndex === 0) {
      lbl.value = 'Hello first time';
   } else {
      lbl.value = sel.options[sel.selectedIndex].value;
   }
}

jsFiddle example