JAVASCRIPT

check if jquery is loaded

$(document).ready(function(){
  if (jQuery) {  
    // jQuery is loaded  
    alert("Yeah!");
  } else {
    // jQuery is not loaded
    alert("Doesn't Work");
  }
});

how to check if jquery is loaded

window.onload = function() {
    if (window.jQuery) {  
        // jQuery is loaded  
        alert("Yeah!");
    } else {
        // jQuery is not loaded
        alert("Doesn't Work");
    }
}

jquery check if document loaded

jQuery offers several ways to attach a function that will run when the DOM is ready. All of the following syntaxes are equivalent:

$( handler )
$( document ).ready( handler )
$( "document" ).ready( handler )
$( "img" ).ready( handler )
$().ready( handler )