Convert the following jquery code to typescript

There are several problems with this code, first off that you are mixing jQuery with JavaScript—the context I am talking about here. For example, see here,

$('#channelType').on('change', function() {
   if (this.value == '1')
   { // ...

this refers to a JavaScript object, not a jQuery one, to refer to that you need to use $(this) object. So I can solve this for you to work in jQuery, provided everything else is fine.

$(document).ready(function(){
   $('#channelType').on('change', function() {
      if ($(this).val() == '1')
      {
          $("#internal").show();
      }
      else
      {
          $("#internal").hide();
      }
   });
});

This should work as jQuery, in case you wanted to make it work. If not, then you need to change a lot of things, starting with the HTML, perhaps your element is a select element, thus that goes like,

<select id="channelType" onchange="channelChanged();">
   <!-- Internal content -->
</select>

Then, somewhere in the JavaScript, you would write the following function to handle the change of value in that element,

function channelChanged() {
    // We can also pass this to the function
    var channelType = document.getElementById("channelType");
    var internalObject = document.getElementById("internal");

    // Change the display of the element.
    if(channelType.value == '1') {
        internalObject.style.display = 'block';
    } else {
        internalObject.style.display = 'none';
    }
}

But again, is this what you want to use? :-)

Read more about onchange event, onchange - Mozilla | MDN[^]