The following list includes guidelines that can help you ensure that custom JS runs as intended:

• Test third-party script before deployment to avoid potential conflicts with internal script.
• Verify that the browsers that you specify can display the customized code, because Pega Platform does not validate custom HTML code.
• Pay attention to the order in which you put the scripts in the code, because the system runs the scripts sequentially.
• Store the JavaScript code in its own separate JS file, because inline JavaScript inserted into a custom section or control requires more maintenance. Separate files also minify the JavaScript source code and enable JavaScript validation and linting.
• For the highest quality and security, reduce the use of HTML fragment rules in application rulesets.
• Attach global scripts to a top-level harness, or include them as part of a static bundle.
• Load a local script for a particular custom section by using the <pega:onlyonce> directive.
• If you use your custom control in multiple sections, load the JavaScript file during the initial loading of the portal by attaching it to the portal harness.
• If the custom control is used infrequently, load the JavaScript file at the end of stream processing by using the <pega:static> JSP tag.