Not a solution for me because I didn’t want to overwrite the MasterPage as part of my feature activation.

Not a solution for me because Delegate Controls are not permitted in the Sandbox.

Not a solution for me because I wanted the script library available on ALL pages.

With SharePoint 2010 there one more technique at your disposal, thanks Wouter for pointing it out to me. This hint then led me to Jan’s post. Its a new type of “CustomAction” that can be included inside a feature along with a “ScriptSrc” attribute which can point to a Javascript library. Eureka! I yelled, and then fell back to earth when I discovered that it pre-appends the SharePoint Hive path to all locations you configure, making it no use to me inside the Sandbox.

Reading Wouters comment more carefully on SharePoint Overflow, I noted that he actually suggested a variation of this custom action, one that allows you to insert a script block instead. I shouted Eureka! again.

Not content with just being able to add my own snippet of Javascript this way, I was sure there would be a way to adapt this to dynamically adding a reference to JQuery. There was, and here it goes:

1. First, create your new SharePoint project, and set it to deploy to the Sandbox.

2. Add a new module to the project, this is where your CustomAction will be created. If you want to deploy your own JS library you can replace the Sample.Txt file with your *.JS and deploy it to the site. Otherwise you can delete it and reference any other JS Library.

3. Now we need to insert the ScriptBlock which is where all the magic happens. I have added comments to describe what happens. This script should be inserted immediately below the:

 

<Elements xmlns="http://schemas.microsoft.com/sharepoint/">

 

<CustomAction

    Location="ScriptLink"

    ScriptBlock="

        //Function that Dynamically Loads the Javascript

        function loadScript(scriptSrc, callbackFunction) {

          //Gets a reference to the Head section, where the Script tage will be inserted

          var headSection = document.getElementsByTagName('head')[0];

          //Creates a new Script tag

          var script = document.createElement('script');

          script.type = 'text/javascript';

          //Sets the source for the script tag to our external library

          script.src = scriptSrc;

          // most browsers

          script.onload = callbackFunction;

          // Fix to ensure support for IE 6-7

          script.onreadystatechange = function() {

              if (this.readyState == 'complete') {

                callbackFunction();

              }

          }

          //Adds the section to the header

          headSection.appendChild(script);

        }

        //Function to test that JQuery has loaded successfully

        //This should be replaced with your own function calls

        function runScript() {

            $(document).ready(function() {  

            alert('jQuery is loaded!!'); });

        }

        //Important, this ensure the scripts execute after SharePoint has done everything it needs to. 

        _spBodyOnLoadFunctionNames.push('loadScript(\'http://ajax.microsoft.com/ajax/jquery/jquery-1.4.2.min.js\', runScript)'); 

    " Sequence="101">

</CustomAction>

In this example we are inserting JQuery from http://ajax.microsoft.com/ajax/jquery/jquery-1.4.2.min.js

3) After completing the above step, you are ready to go. You now simply need to deploy your solution, and then refresh your home page. If everything worked correctly you should get something like the below.

I have packaged up my complete solution, and its available for you to download, grab it from here:
http://www.zevenseas.com/go.aspx?ScriptInTheSandbox=Download