Don’t prevent the browser’s default behavior corresponding to the Alt key

[yuheiy]

In most browsers, clicking links with the Alt key has a special behavior, for example, Chrome downloads the target resource. As with other modifier keys, the router should stop the original navigation to avoid preventing the browser’s default behavior.

When users click a link while holding the Alt key together, the browsers behave as follows.

Windows 10:

Browser	Behavior
Chrome 84	Download the target resource
Firefox 79	Prevent navigation and therefore do nothing
Edge 84	Download the target resource
IE 11	No impact

macOS Catalina:

Browser	Behavior
Chrome 84	Download the target resource
Firefox 79	Prevent navigation and therefore do nothing
Safari 13	Download the target resource

Before submitting the PR, please make sure you do the following

• It's really useful if your PR relates to an outstanding issue, so please reference it in your PR, or create an explanatory one for discussion. In many cases features are absent for a reason.
• This message body should clearly illustrate what problems it solves. If there are related issues, remember to reference them.
• Ideally, include a test that fails without this PR but passes with it. PRs will only be merged once they pass CI. (Remember to npm run lint!)

Tests

• Run the tests tests with npm test or yarn test)

[benmccann]

It might be a good idea to submit this PR to page.js as well: https://github.com/visionmedia/page.js/blob/master/page.js#L748

• they're more familiar with this block of code and it would give confidence that this is the correct fix
• it would help us keep this block of code in sync with the upstream version

[yuheiy]

I’ve already submitted. visionmedia/page.js#568

[Conduitry]

Does the "No impact" for IE 11 mean that typically alt-clicking a link performs regular navigation, and that with this change we'd no longer be intercepting these clicks and it would perform a regular page navigation instead of an SPA-type navigation?

Even if so, I think it's probably overall a good idea to make this change - I just want to be clear on what its effect is.

[yuheiy]

That’s right. In IE 11, alt-clicking has the same behavior as when the user is not using alt.

[yuheiy]

So IE 11 performs a regular page navigation.