Dynamically loading a script changes its behaviour

Question 1

I think I figured out a workaround as well - paper.PaperScript.load() or to elaborate:

<html>
    <head>
        <script src="http://code.jquery.com/jquery-latest.js"></script>
        <script>
            $(document).ready(function () {
                $("#jq").text("jQuery is now loaded.")
                var paperUrl = 'http://cdnjs.cloudflare.com/ajax/libs/paper.js/0.22/paper.js';
                var lateLoad = function() {
                    $.getScript(paper_url, function() { 
                        $("#pp").text("Paperjs is now loaded.");
                        paper.PaperScript.load(); // <-- The fix!
                    });
                };
                setTimeout(lateLoad, 1000);
                //$.getScript(paperUrl, function() {
                //    $("#pp").text("Paperjs is now loaded.");
                //});
            });
        </script>
    </head>
    <body>
        <script type="text/paperscript" canvas="myCanvas">
            $('body').css({"background-color": "#999"});
            alert('hi!');
        </script>
        <p id="jq">jQuery NOT loaded yet.</p>
        <p id="pp">Paperjs NOT loaded yet.</p>
    </body>
</html>

That causes paperscript to scan for all the paperscripts. I found it at https://github.com/paperjs/paper.js/blob/master/src/core/PaperScript.js#L270 while googling for "paperscript" in the github repo. Though it still doesn't explain why paper doesn't do the load() on its own when dynamically loaded.

EDIT - I understand what went wrong. It's related to https://github.com/jquery/jquery/blob/master/src/core.js#L768 because paperjs doesn't check if the window loaded event had already fired i.e document.readyState === "complete". I submitted a pull request to paperjs https://github.com/paperjs/paper.js/pull/156

Question 2

I think it is easier to load it via require.js. All you need is a require.config object, defined in e.g. main.js:

requirejs.config({
    paths : {   
        'jquery' : "path/to/jquery"
        'paper' : "path/to/paper"
    },
    shim: {
        'jquery' : {
            exports: 'jQuery'
        },
        'paper' : {
            exports: 'paper'
        }
    }
});

You will need to load require.js with the above config via the data-main attribute:

<script data-main="scripts/main.js" src="scripts/require.js"></script>

Then you define a module (e.g. 'paperStuff') where your paper logic will be:

define(['jquery', 'paper'], function($, paper) {
   // do some cool stuff
});

When you want to load your paperStuff, you just do

var paperStuff = require('paperStuff');
...

Question 3

Move your paperscript code into an external file (i.e. pstest.js) and modify your lateLoad to:

var lateLoad = function() {
    $.getScript('http://cdnjs.cloudflare.com/ajax/libs/paper.js/0.22/paper.js',
    function() {
      $("#pp").text("Paperjs is now loaded.");
      $.getScript("pstest.js");
    } )
}