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vite-plugin-lit

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Version 0.19.0

Lit rendered on the server with @lit-labs/ssr now works with the plugin: edits hot-patch hydrated components and reach the next server render, shared sheets arrive styled, and the Components tab shows where hydration stands. A new SSR example covers dev, production builds and StackBlitz. Lit Inspector gains a Lit tab in the Elements panel and reads Custom Elements Manifests from more places, and the DevTools flag double renders. Nothing needs action to upgrade.

Added

  • Server-rendered Lit works in the dev server. With @lit-labs/ssr in your Vite server, an edit patches hydrated components in place and the next server render uses the new code instead of failing because the tag is already defined. A ?css-sheet renders into the declarative shadow root, so the page arrives styled, and its edits restyle hydrated components. A defer-hydration component edited before it wakes renders the new template, and a page whose HTML predates an edit renders that component once in the browser instead of failing to hydrate. The new SSR guide shows the setup, and Troubleshooting covers the dock’s socket in middleware mode.
  • The Components tab shows hydration state. A server-rendered component is marked deferred while defer-hydration holds it back, not hydrated until its first update, and SSR the moment it hydrates, in the tree and the details pane.
  • An SSR example, on StackBlitz too. Open it from the README or the docs’ Demos page: the counter arrives as server HTML, hydrates, and keeps its count through an edit, with the DevTools dock connected.
  • Server-rendered pages in production builds, with the Lit panel. The SSR guide and example cover a production build served without Vite: shared ?css-sheet styles arrive inlined, and the Lit panel attaches through lit-devtools dev with each element’s hydration state.
  • The Lit panel works without Vite DevTools. With timeline: true and no DevTools(), the dev server serves the panel at /__lit/ and prints its address, instead of only warning that the panel never mounted.
  • A Lit tab in the Elements panel. The browser extension adds a Lit tab to the Elements sidebar, beside Styles and Computed, showing the properties, state, slots, parts and source links of the Lit element you select there.
  • Double renders are flagged. An update that a component’s own previous update scheduled, usually because updated() set a property, is marked re-rendered in the Updates tab and 2× in the Timeline list, and lit_update-summary reports it as selfCaused. The Components tab’s Warnings count how many times the recording shows an element re-rendering itself, also under a production build.
  • The Components tab counts dispatched events. With the Custom events layer on, a Dispatched section lists how many times the selected element dispatched each event type during the recording.
  • Properties show which class declared them. For a component that extends a base class or uses mixins, the Properties and State tables group their rows under the declaring class, the element’s own first.
  • Component docs include members from your mixins. For a component written as extends Sized(Base), the Components tab lists what your project’s Sized mixin adds, marked as inherited from it, and still reaches Base past a package mixin such as SignalWatcher.
  • Agents can set component properties. The new lit_set-prop tool sets a reactive property, or a field inside the object it holds, on a live element and answers with the element’s details afterwards. Agent edits land as overrides in the panel, where you can switch them off or clear them.
  • Lit Inspector can pause on an update or a property change. Arm update or render on the selected element, or the pause toggle on one of its properties, and the page stops in the debugger when it happens.
  • Lit Inspector finds more Custom Elements Manifests. When a page links none, the Lit tab looks for every custom-elements.json beside the page’s scripts and offers them, so Web Awesome’s docs show component documentation with one click. Manifests on another site, such as a CDN, work once Chrome is granted access to it, through an Allow access button for a linked one.
  • Choose the manifests Lit Inspector reads. The Settings tab’s Component docs section lists the page’s linked manifests, the ones found and the ones you add by URL, such as /dist/custom-elements.json. Each can be switched off, ignored and reset, or moved up and down; the first switched-on one that describes a component supplies its docs.
  • The extension shows where an element is rendered. On a page without the Vite plugin, the details pane’s rendered row names the template tag that created an element, found by the template’s text in the page’s sources, and in Chrome a click opens it in the Sources panel.
  • Read component docs without hovering. Turn on “inline descriptions” under Components in the Settings tab, and every documented property, attribute, slot and part shows its description under its row.
  • unoSheet() works with presetWind4. Pass preflights: true to keep Wind4’s theme variables and @property rules in the shared sheet; drop the reset at the preset with presetWind4({preflights: {reset: false}}).
  • Context consumers waiting for a provider say so. A subscribing consumer that no provider has answered yet reads “waiting for a provider” instead of linking to a provider that never answered it, and links as soon as a ContextRoot replays its request.

Changed

  • The Settings tab no longer lists env var names. Hints name the plugin option alone, the reset button reads “Reset overrides”, and a value set from the environment still shows its “(env)” badge.

Fixed

  • Hiding the panel clears what it drew on the page. Collapsing the dock, closing DevTools with the browser extension, or closing a panel opened as its own tab now takes down the anatomy overlay, hover outline and breakpoints and stops Live, instead of leaving them until the page reloads. The overlay comes back when the dock opens again.
  • Slotted context consumers link to the right provider. A consumer slotted into a component whose shadow tree provides the context now links to that provider, instead of to none or to one further out.
  • A provider’s details follow a value set directly. Setting a context provider’s value with setValue, without its host updating, refreshes the selected provider’s row right away instead of on its next update.
  • A component whose constructor threw is no longer called “not Lit”. The Components tab marks it not upgraded and says its constructor probably threw, instead of claiming another library defined it.
  • The Anatomy “not rendered” list follows the page. A light child added with a slot name the element doesn’t have, or renamed to one, shows up without reselecting the element.
  • The Updates tab’s equal-content badge shows its icon again. The badge that flags a property changed to a new reference with equal content rendered as a bare number.
  • lit-devtools mcp finds dev servers behind your own HTTP server. When Vite runs in middleware mode with your server passed in, the plugin registers that server’s real port instead of probing 5173 and warning that discovery is unavailable.