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问题:

I am attempting to check if my Jquery Library is loaded onto my HTML page. I am checking to see if it works, but something is not right. Here is what I have:

<html xmlns=\"http://www.w3.org/1999/xhtml\">
    <head>
        <script type=\"text/javascript\" src=\"/query-1.6.3.min.js\"></script>
        <script type=\"text/javascript\">
          $(document).ready(function(){
             if (jQuery) {  
               // jQuery is loaded  
               alert(\"Yeah!\");
             } else {
               // jQuery is not loaded
               alert(\"Doesn\'t Work\");
             }
          });
        </script>

回答1:

something is not right

Well, you are using jQuery to check for the presence of jQuery. If jQuery isn\'t loaded then $() won\'t even run at all and your callback won\'t execute, unless you\'re using another library and that library happens to share the same $() syntax.

Remove your $(document).ready() (use something like window.onload instead):

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

回答2:

As per this link:

if (typeof jQuery == \'undefined\') {
    // jQuery IS NOT loaded, do stuff here.
}

there are a few more in comments of the link as well like,

if (typeof jQuery == \'function\')
//or
if (typeof $== \'function\')

and

if (jQuery) {
    alert(\"jquery is loaded\");
} else {
    alert(\"Not loaded\");
}

Hope this covers all good ways to get this thing done!!

回答3:

if (\'undefined\' == typeof window.jQuery) {
    // jQuery not present
} else {
    // jQuery present
}

回答4:

Just a small modification that might actually solve the problem:

window.onload = function() {
   if (window.jQuery) {  
       // jQuery is loaded  
       alert(\"Yeah!\");
   } else {
    location.reload();
   }
}

Instead of $(document).Ready(function() use window.onload = function().

回答5:

You can do this fast on the console-tab when inspecting your webpage.

E.g:

$ === jQuery

If it returns true it means it\'s loaded.

回答6:

A quick way is to run a jQuery command in the developer console. On any browser hit F12 and try to access any of the element .

 $(\"#sideTab2\").css(\"background-color\", \"yellow\");

$\"enter$

回答7:

You can just type window.jQuery in Console . If it return a function(e,n) ... Then it is confirmed that the jquery is loaded and working successfully.

Checking if jquery is loaded using Javascript

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Checking if jquery is loaded using Javascript

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