enhancement:add error handling

[tejaswini22199]

Related Issue

issue #39

Proposed Changes

• added an alert in visualization.js
• modified class to className in java script files

  Additional Info

• any additional information or context

Checklist

• [ ] Tests
• [ ] Translations
• [ ] Documentation

Screenshots

Original	Updated
original screenshot	updated screenshot

[tejaswini22199]

@adityabisoi could you please review it and tell me if any modifications are needed

[tejaswini22199]

@adityabisoi could you please review