For webpages:

• You can paste your HTML into a file, save it as "some_name.html" and open it in your web browser.
• For more details, read the article on Developing Webpages outside Khan Academy.

For ProcessingJS programs:

• You can make a webpage, including the ProcessingJS library in it, and put your program code in it, and open it in a browser. Try using the template here to get started.
• Note there are differences between our version of ProcessingJS and the linked version.
• For more details, read the article on Using ProcessingJS outside Khan Academy.