feat(b-nav-item-dropdown): improve default handling of dropdown toggle link (closes #3942)

[jacobmllr95]

Describe the PR

This PR improves the link handling of <b-nav-item-dropdown> by assining the user provided ID as the toggle link href has link.

When id prop isn't set (defaults to null) the href for the <b-link> i set to #. If an id is provided, then the href for <b-link> will be set to #{id}. This way, before the page is hydrated, the link will just scroll to the A tag (which should already be in view and hence not scroll) rather than scrolling to the top of the page.

Closes #3942.

PR checklist

What kind of change does this PR introduce? (check at least one)

• Bugfix (fixes a boo-boo in the code) - fix(...), requires a patch version update
• Feature (adds a new feature to BootstrapVue) - feat(...), requires a minor version update
• Enhancement (augments an existing feature) - feat(...), requires a minor version update
• ARIA accessibility (fixes or improves ARIA accessibility) - fix(...), requires a patch or minor version update
• Documentation update (improves documentation or typo fixes) - chore(docs), requires a patch version update
• Other (please describe)

Does this PR introduce a breaking change? (check one)

• No
• Yes (please describe since breaking changes require a minor version update)

The PR fulfills these requirements:

• It's submitted to the dev branch, not the master branch
• When resolving a specific issue, it's referenced in the PR's title (i.e. [...] (fixes #xxx[,#xxx]), where "xxx" is the issue number)
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If new features/enhancement/fixes are added or changed:

• Includes documentation updates
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• New/updated tests are included and passing (required for new features and enhancements)
• Existing test suites are passing
• CodeCov for patch has met target (all changes/updates have been tested)
• The changes have not impacted the functionality of other components or directives
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[codecov]

Codecov Report

Merging #5344 into dev will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##               dev     #5344   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          281       281           
  Lines         8825      8828    +3     
  Branches      2505      2505           
=========================================
+ Hits          8825      8828    +3     

Flag	Coverage Δ
#unittests	100.00% <100.00%> (ø)

Impacted Files	Coverage Δ
src/mixins/id.js	100.00% <ø> (ø)
src/components/nav/nav-item-dropdown.js	100.00% <100.00%> (ø)

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[jacobmllr95]

@scyclops Can you create a CodeSandbox based on this template with a minimal reproduction of your Nuxt.js setup to confirm that the problem is resolved?

[tmorehouse]

I just checked in the PR preview, and checked the SSR rendered source for the version dropdown in the docs nav, and it renders the following (before hydration):

a aria-haspopup="true" aria-expanded="false" href="#" target="_self" class="nav-link dropdown-toggle mr-md-2"><span>Pull Request</span></a>

So the href="#" is still there before Vue kicks in.

Perhaps we could try and use a <button> element for the dropdown toggle in b-nav-item-dropdown and see how the Bootstrap v4 styling work on it.

Edit:

Just tested rendering a native <button> instead of the <a> and just had to add classes border-0 bg-transparent to it to make it look correct.

[jacobmllr95]

@tmorehouse Or we just expose href as prop as suggested in the issue.
It works fine for most of the users and for those who need to adjust it would have the possibility.

[tmorehouse]

We would still need to make sure event.preventDefault() is called... <b-link> doesn't do this automatically when HREF is anything other than #.

Another option would be to set an ID on the <a> and set href to point to this ID (unfortunately we cant use safeId() auto-ID as it only runs client side)

[jacobmllr95]

The toggle() method in dropdownMixin calls event.preventDefault() which the click event on the <b-link> is assigned to. So we should be fine.

[tmorehouse]

Hmm, we should be adding role="button" to the rendered <a> tag that way an HREF won't confuse screen reader users.

How about we add an ID prop. This ID will be added to the link and then used as the href,
that way only hash HREFs are generated:

<a :id="id" :href="'#' + id'" role="button">

This way, before the page is hydrated, the link will just scroll to the A tag (which should already be in view and hence not scroll). If hte ID is null/blank/undefined, it would just render a plain href="#", which is the default behaviour.

This way the purpose of href as a prop wouldn't be confusing (and needing long explanation as to its use).

EDIT:

Actually we do have safeId in there, and we do generate an ID for the toggle button <a> tag... we could set this as the href (by pre-pending with #)

As long as the user supplies a unique ID, the href will be valid during SSR and before hydration