Alert on repeated item

[didemydn]

For an example of how to fill this template out, see this Pull Request.

Description

Users shouldn't be able to add an empty item to their list, or add the same item twice. If they try to do this, we need to show them an error message that explains the problem. This way, we’ll prevent some clutter in their lists.

Related Issue

closes #10

Acceptance Criteria

Acceptance criteria

• Show an error message if the user tries to submit an empty item
• Show an error message if the user tries to submit a new item that is identical to an existing name. For instance, if the list contains apples and the user adds apples.
• Show an error message if the user tries to submit a new item that matches an existing name with punctuation and casing normalized. For instance, if the list contains apples and the user adds aPples or apples, or a pples.
• The user’s original input is saved in the database

Updates

Before

List view
You can add an item if there is already one in the list. exp oat and Oat,

After

- an error message if the user tries to submit an empty item

- an error message if the user tries to submit a new item that is identical to an existing name

- an existing name with punctuation and casing normalized

Testing Steps / QA Criteria

npm start
manageList view
Add an item to a list

[github-actions]

Visit the preview URL for this PR (updated for commit cf0fcc0):

https://tcl-78-smart-shopping-list--pr27-dc-tc-alert-on-repea-ib43nvjo.web.app

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[eva-lng]

The feature works well, great job! I like the use of regex, makes the code look concise and clean.

[GrannyYetta]

Hi Didem and Tataw, the feature works well for me. It looks great and the comments are very helpful!

Fun fact: I get the "fill out all the fields" messages in Spanish.

[vivitt]

Thanks for your work team 🚀
The new feature works well, and your code looks great! Great job ⚡️

Just a suggestion for a possible future improvement: normalizing all the names that are stored, so that when we display items in the list they all have consistent capitalization.