How to detect textbox change event from javascript

Question

I have a textbox asp.net server control. I am modifying the value of textbox from javascript i want to detect when the textbox text is changed. I tried onchange event which gets called on lost foucs when the text changes. But in my case i an changing text from Javascript. how can i achieve this?

Answer 1

Updating the value property won't trigger the change event. The change event is triggered by the user.

You can either write a function which changes the value and does whatever else you need to do...

function changeTextarea(str) {
   document.getElementById('a').value = str;
   // Whatever else you need to do.
}

...or poll the textarea's value...

(function() {
   var text = getText();   
   var getText = function() {
      return document.getElementById('a').value;
   }  

   setInterval(function() {
      var newtext = getText();
      if (text !== newText) {
          // The value has changed.
      }
      text = newText; 
   }, 100);
})();

...or explicitly call the onchange() event yourself.

document.getElementById('a').onchange();

(Assuming you set the event up with onchange property.)

The workarounds are not terribly great solutions. Either way, you need to do some intervention to trigger extra code when updating a textarea's value property.