Allow frontend method execution on Block.load event

[codedealer]

Description

Please include:
Adds _js as an optional parameter to the load event similar to other events

Closes: #2105

Checklist:

• I have performed a self-review of my own code
• My code follows the style guidelines of this project
• I have commented my code in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[abidlabs]

Thank you for the PR @codedealer! LGTM

[codedealer]

@abidlabs Hey, I changed the tests to account for the changed js argument (optional value from bool to none). Let me know if I need to do anything else.

[abidlabs]

Thank you so much @codedealer for the contribution. Looks ready to merge!