Replace deprecated substr() with slice() in the codebase

[sarraf1996]

Summary

The substr() method is deprecated in JavaScript and may cause issues or warnings in future versions. To ensure better compatibility and prevent potential runtime issues, we should replace all occurrences of substr() with slice().

Details

Currently, the following functions in index.js file contain instances of substr():

• JSONCookie(str) {}
• signedCookie (str, secret) {}

These should be refactored to use slice() instead.

Why It Should Be Fixed

JavaScript's substr() method has been deprecated. Refactoring to use slice() will future-proof the code and prevent potential issues in modern JavaScript environments. This change is necessary for compatibility with new ECMAScript standards and best practices.

Suggested Solution

Replace substr() with slice() in all occurrences.

References

For more details on the deprecation of substr(), see the MDN documentation: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substr

[gitdevjin]

if it is still open, can I try to work on this?

[IamLizu]

Hey @gitdevjin 👋

It appears we have a open PR for this one already. Could you please review the PR if you are interested? #111

[gitdevjin]

@IamLizu
Oh, I am sorry. I think I didn't check the PR.
Yeah I think someone has already made a PR for this issue, and I will review it.
thanks! :)

[sarraf1996]

@gitdevjin Thanks for reviewing my pull request. Actually, I only created the PR post creating this issue thread.

@IamLizu Thank you for your review and approval. The pull request is now ready for merging. Please proceed if there are no additional concerns or outstanding issues.