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Asked: 2026-05-11T19:20:32+00:00

I am using JQuery to inject dynamically script tags in the body tab of

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I am using JQuery to inject dynamically script tags in the body tab of a webpage. I got something like : 

function addJS(url) {
  $("body").append('<script type="text/javascript" src='+url+'></script>'); 
}

I add several scripts this way, and try to use them right after. E.G :

lib.js 

function core() {...}
alert("I'am here !");

init.js

addJS("lib.js");
c = new core();

test.html

<html>
  <head>
    <title>test</title>        
    <script type="text/javascript" src="init.js"></script> 
  </head>
  <body>
     Hello
  </body>
</html>

Loading test.html pops up “I’m here” and then ends up with an error “core is not defined”. Of course merging both of the JS files will make them work perfectly.

I just don’t get it o_O.

EDIT

I simplified this example, but Jeff answer made me understand that it was a mistake. So here are some details :

init.js is not in the head of test.html when it reload because I inject it with a code exectuted on a bookmarklet.

So the real execution process is the following :

reload test.html > run the bookmarklet > jquery and init.js are inserted > lib.js is inserted

Sorry for the confusion.

EDIT 2

Now I have the solution to my problem (that was quick :-)) but I am still interested to the answer to my question. Why does this go wrong ?

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1 Answer

  1. Editorial Team

    You get the “core is not defined” error because the scripts are loaded asynchronous. Which means that your browser will start loading lib.js in the background, and continue executing init.js, and then encounter “new core()” before the lib.js has finished loading.

    The getScript function has a callback that will be triggered after the script is finished loading:

    $.getScript('lib.js', function() {
    var c = new core();
});
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