vue-hmr-repro

HMR only works if the component has an active instance. A regression was introduced in 3.2.11. 3.2.10 behaves as expected.

Most users experience this issue when using vue-router, as no full reload occurs, and is not unusual to navigate between pages.

It can happen in different scenarios, for example, a component that is conditionally displayed. If the user modifies the component file when the condition is false, and then the condition becomes true, the rendered component is outdated and won't reflect current changes until a page reload or another HMR update is sent.

Replication Steps

• Install packages
• Run npm run dev
• Visit http://localhost:3000/about
• Comment <Welcome/> in src/views/Home.vue
• Navigate to the Home page
• The <Welcome/> component is still displayed

Explanation 🐞

When the modified page component:

• is the current route, it has an active instance, so HMR works.
• is not the current route, it has no active instances, so HMR does nothing.

As a result, when modifying a component that is not the current route, the HMR update is sent as usual, but it doesn't update the module.

Then, when the route for the modified component is visited, the original module is used, which doesn't include the changes since it was never updated by HMR.

More Subtle for Dynamic Imports

To replicate the bug with lazy routes, the dynamic import must have been resolved.

For example, the bug will not occur in this sequence:

• Navigate to the Home page
• Add an exclamation mark to the text in src/views/About.vue
• Navigate to the About page using the nav link
• The modified text is displayed

But, if you proceed to:

• Navigate again to the Home page using the nav link
• Add another exclamation mark to the text in src/views/About.vue
• Navigate to the About page using the nav link
• The last change is not there