CODEWITHSUNDEEP
javascriptjquery
Jay
Jay

Reputation: 806

How Do I Add jQuery To Head With JavaScript?

I am trying to include jQuery to an HTML page conditionally. It only needs to be added if it doesn't exist yet.

I am using the following code near the top of my body tag to inject a script tag that includes the jQuery library in the head.

<script type="text/javascript">

    if (typeof jQuery === 'undefined') {
        alert('now adding jquery');
        var head = document.getElementsByTagName("head")[0];
        script = document.createElement('script');
        script.type = 'text/javascript';
        script.src = 'https://ajax.googleapis.com/ajax/libs/jquery/1.6.4/jquery.min.js';
        head.appendChild(script);
        if (typeof jQuery === 'undefined') {
            alert('jquery still not present :(');
        }
    } else {
        alert('jquery already present');
    }
</script>

When I execute it, I get the message that jQuery is still not present after adding it. The script tag does correctly show up in the loaded page's source.

Trying to make use of jQuery a little further down below in my page, confirms that jQuery is indeed not working. As expected, Chrome's JavaScript console says '$ not defined'.

How can I get this to work?

Upvotes: 3

Views: 12501

Answers (3)

Bizniztime
Bizniztime

Reputation: 1036

You are not waiting for the script to load after appending it to document

Try this code before appending:

   function helper(){
        if (typeof jQuery === 'undefined') {
            alert('jquery still not present :(');
        }
   };

   script.onreadystatechange= function () {
      if (this.readyState == 'complete') helper();
   }
   script.onload= helper;

I've found it here if you want to know more

Also there are loaders like StealJS or YepNope

Upvotes: 2

pimvdb
pimvdb

Reputation: 154818

A script loads asynchronously. This means its contents are not directly available after appending the element.

Use onload instead:

script = document.createElement('script');

script.onload = function() {
    // jQuery is available now
};

script.type = 'text/javascript';
script.src = 'https://ajax.googleapis.com/ajax/libs/jquery/1.6.4/jquery.min.js';

head.appendChild(script);

Upvotes: 4

Marco Johannesen
Marco Johannesen

Reputation: 13134

Boilerplate uses this method to test if jQuery is loaded by google, if not use local:

  <script src="//ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js"></script>
  <script>window.jQuery || document.write('<script src="js/libs/jquery-1.6.2.min.js"><\/script>')</script>

Seems like what you want to achieve :)

Upvotes: 2

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