onchange an id in jquery code example

Example 1: jquery onchange input value

$("input").change(function(){
  alert("The text has been changed.");
});

Example 2: jquery detect change in textarea content

$('#textareaID').bind('input propertychange', function() {

      $("#yourBtnID").hide();

      if(this.value.length){
        $("#yourBtnID").show();
      }
});