• #5044 0d0170e87b06edd8295a31893c820162d0f16a23 Thanks @ava-cassiopeia! - Make ClassInfo mutable

• #5064 bc2926eb99a97ef4efb7eefbe133d6a33f216e18 Thanks @brysonbw! - Add SVGElement to the render() container type, allowing SVG elements to be used as render roots without type errors.

• #5035 c36626b8018ca78a47e61abdfa5b5904bed06843 - Make some of our directives generic, so that their DirectiveResult types capture everything needed to infer their render types. This is useful in template type checking.

• #4997 aea85e24 - Update README

• #4988 6792b7ef Thanks @ADNolan! - Adjusted the comparison to use the name property of the _$resolve function and the resolveOverrideFn in private ssr support to prevent duplicated patching of the directive class.

• #4975 43a3f4dc - Remove some redundant code from removePart()

• #4901 c9160405 Thanks @maxpatiiuk! - Dev mode warnings are now emitted on the next microtask after package import, allowing for a wider opportunity to suppress the warnings by consumers.

• #4956 0a9bc720 Thanks @louis-bompart! - Import barrels explicitly for compatibility with modern Node resolution w/ ESM

• #4782 99703a03 - Revert the Terser plugin for Rollup to rollup-plugin-terser from @rollup/plugin-terser due to a bug that prevented our minified name prefixing from working.

• #4637 feccc1ba - Add MathML support with the mathml template tag

• #4646 abf30b3e - The value provided by the ref() directive will always be undefined when the element is disconnected.

• #4570 bd881370 - Fix the lit-html marker length to be consistently 9 characters.

• #4523 1a32b61e - Add a DEV_MODE error to catch duplicate attribute bindings that otherwise create silent errors.

• #4485 57b00630 - Add "browser" export condition entrypoints to any package.json files with "node" export conditions. This fixes Node test runners emulating browser environments that were incorrectly loading the "node" entrypoints instead of the browser code.

• #4515 dca963f7 - Fix a memory leak when patching directive constructors for SSR.

• #4409 1af7991c - asyncReplace correctly re-renders when value is unchanged (#4408)

• #4309 949a5467 - Adds two new types: UncompiledTemplateResult and MaybeCompiledTemplateResult. Currently UncompiledTemplateResult is the same as TemplateResult, and MaybeCompiledTemplateResult is the union of the compiled and uncompiled types.

• #4345 02b8d620 - Add a dev mode warning if a static value such as literal or unsafeStatic is detected within the non-static html tag function. These should only be used with the static html tag function imported from lit-html/static.js or lit/static-html.js.

• #4240 edf998c9 Thanks @remziatay! - Improved the type inferece of the choose() directive to properly restrict the case type inferred from provided value. Note: If this change creates a type error in your code, there must have been an unreachable case that can be removed, or the type of your value might be missing a valid case in the union.

• #4310 8f674ab3 Thanks @megheaiulian! - The when() directive now calls the case functions with the provided condition value as an argument. This allows the narrowing of types for the condition value based on its truthiness when used as a parameter for the case function.

• #3756 f06f7972 - Drop IE11 support

• #3759 1db01376 - Use replaceWith() for SVG templates

• #3765 92cedaa2 - Remove experimental hydrate modules. These are available from @lit-labs/ssr-client.

• #3751 dfd747cf - Simplify lit-html attribute handling for standards-compliant browsers that iterate attributes in source order

• #3750 c3e473b4 - Use toggleAttribute() to simplify boolean attribute parts

• #4141 6b515e43 - Update TypeScript to ~5.2.0

• #3762 23c404fd - Remove Lit 1 -> Lit 2 migration warnings

• #4081 d27a77ec - Sync from last stable release

• #4141 6b515e43 - Update TypeScript to ~5.2.0

• #3751 dfd747cf - Simplify lit-html attribute handling for standards-compliant browsers that iterate attributes in source order

• #3759 1db01376 - Use replaceWith() for SVG templates

• #3750 c3e473b4 - Use toggleAttribute() to simplify boolean attribute parts

• #3765 92cedaa2 - Remove experimental hydrate modules. These are available from @lit-labs/ssr-client.

• #3756 f06f7972 - Drop IE11 support

• #3762 23c404fd - Remove Lit 1 -> Lit 2 migration warnings

• #3814 23326c6b - Update to TypeScript v5.0

• #3993 e2c50569 - Fix return type of isTemplateResult helper to include the CompiledTemplateResult and fix the cache directive to work correctly with CompiledTemplateResults. Also add an explicit isCompiledTemplateResult helper.

• #3968 5bb40831 - Allow undefined to be passed to the ref() directive

• #3969 7d8d4a15 - Make RefOrCallback generic like Ref

• #3987 bb2560f1 - Change the h field of CompiledTemplates to a TemplateStringsArray preventing the spoofing of CompiledTemplates by JSON injection attacks. This should not be a breaking change for most users unless you're using CompiledTemplates. This is a necessary security fix, similar to #2307.

• #3888 0f30e6fb - Fix a memory leak cause by lit-html's shared TreeWalker holding a reference to the last tree it walked.

• #3825 343187b1 - static-html no longer adds an item to TemplateResult's value array for the last consumed static value. This fixes an error with server-side rendering of static html.

• #3766 4431cbb8 - Fix styleMap initial render of mixed-case custom props

• #3788 88fe0390 - Allow numbers to be used as values in styleMap()

• #3768 7c1191da - Fix styleMap's handling of important flags

• #3720 575fb578 - lit-html/experimental-hydrate.js and lit-element/experimental-hydrate-support.js have been moved to @lit-labs/ssr-client.

  The modules in the original location have been marked deprecated and will be removed in a future version.

• #3667 e00f6f52 - [SSR only] Improved how nodes with attribute/property/event/element bindings are rendered in SSR, to avoid adding comments inside of "raw text elements" like <textarea>. Fixes #3663.

  Note: @lit-labs/ssr and lit-html must be updated together.

• #3615 4d698430 - Don't throw in ChildPart.parentNode if the parentNode is null

• #3583 88a40177 - [SSR only] Add more detail to some hydration errors

• #3526 65e56655 - Disable ShadyDOM noPatch in Node dev build. This fixes the issue of throwing due to undefined window.

• #3522 72fcf0d7 - When running in Node, Lit now automatically includes minimal DOM shims which are sufficient for most SSR (Server Side Rendering) use-cases, removing the need to import the global DOM shim from @lit-labs/ssr.

  The new @lit-labs/ssr-dom-shim package has been introduced, which exports an HTMLElement, CustomElementRegistry, and default customElements singleton.

  The existing @lit-labs/ssr global DOM shim can still be used, and is compatible with the new package, because @lit-labs/ssr imports from @lit-labs/ssr-dom-shim. Importing the global DOM shim adds more APIs to the global object, such as a global HTMLElement, TreeWalker, fetch, and other APIs. It is recommended that users try to remove usage of the @lit-labs/ssr DOM shim, and instead rely on the more minimal, automatic shimming that @lit/reactive-element now provides automatically.

• #3507 b152db29 - lit-html and reactive-element now include development Node builds with unminified code and dev warnings.

• #3318 21313077 - Adds an isServer variable export to lit and lit-html/is-server.js which will be true in Node and false in the browser. This can be used when authoring components to change behavior based on whether or not the component is executing in an SSR context.

• #3223 5a65ca97 - Use existing document in Node build

• #3156 ae6f6808 - Lit and its underlying libraries can now be imported directly from Node without crashing, without the need to load the @lit-labs/ssr dom-shim library. Note that actually rendering from a Node context still requires the @lit-labs/ssr dom-shim, and the appropriate integration between @lit-labs/ssr and your framework/tool.

• #3003 daddeb34 - Lit's async-directive now re-exports everything from the directive module.

• #3199 0725fdb4 - In DEV_MODE, render a warning instead of rendering a template's host in the template.

  Most commonly this would happen when rendering ${this} in a LitElement's template, which has the counterintuitive behavior of removing the element from the DOM, because when rendering the element's template we attach it into its own shadow root, which removes it from the DOM, causing it simply disappear. This is especially problematic with a fast HMR system.

• #3186 3766ae4c - StaticValue interface type is now exported.

• #3130 1f0567f1 - Export the underlying type of the keyed directive.

• #3132 2fe2053f - Added "types" entry to package exports. This tells newer versions of TypeScript where to look for typings for each module.

• #2849 b12e8d93 - Expand documentation for render and TemplateResult.

• #2952 a78cc3b7 - Fix SSR hydration bug relating to and other void elements having attribute bindings.

• #2847 79d82385 - Fix typo in API docs for live() directive.

• #2828 b3b6bc33 - Remove private Lit 2 migration helpers: INTERNAL and clearContainerForLit2MigrationOnly. This logic is no longer depended on.

• #2732 3e181bcb - Enforce use of file extensions in imports. Fixes an issue with older TypeScript compilers.

• #2657 a6069c40 - Remove readonly restriction from StyleInfo interface as addition, deletion, and updating of styles is valid. Expanded styleMap documentation with links to lit.dev.

• #2642 badc532c - Add an additional security brand check to StaticValues; Similar to #2307

• #2691 171143bd - Fixes ref bug when auto-bound class method used as a callback could incorrectly receive undefined.

• #2661 9a3a38cd - Give a clearer error message when rendering into null/undefined

• #2646 365cd09a - Clarify that hacking around the template strings array brand error can create security vulnerabilities.

• #2635 ae358703 - Make the event debug logger lazier, doing even less work (with no side effects) even in dev mode unless the page has opted in.

• #2401 2c9d0008 - Added a devlog events system that may be used for debugging and visualizing Lit's internals.

• #2498 2a1dc7a1 - Replace 'rare' with 'invalid' in svg tag function JSDocs.

• #2459 23df9d45 - Fix bindings inside of <title> elements

• #2479 89560520 - Expand JSDocs for the svg tagged template literal (TTL). The new documentation makes it more clear that the svg tag function should only be used for SVG fragments, and not for the <svg> HTML element.

• #2399 5ac025bf - Correct typo in async-directive module comment

• #2410 b9a6962b - Correct the link path of CONTRIBUTING.md in README.md files

• #2388 5860533f - Fix choose directive jsdoc code example.

• #2337 fcc2b3d0 - Add a keyed(key, value) directive that clears a part if the key changes.

• #2335 d319cf5f - Add when, map, join, and range directives.

• #2341 1d563e83 - Add choose() directive

• #2307 221cb0a9 - Added an additional check to prevent spoofing of internal lit types in data bindings.

• #2146 8bb33c88 - Work around a Chrome bug with trusted types: https://crbug.com/993268

• #2236 5fc3818a - Prevent polyfillSupport.noPatchSupported from implicitly being any. Deduplicate types for DevMode-suffixed polyfill support functions.

• #2152 ba5e1391 - Replace dynamic name lookups for polyfill support functions with static names.

• The templateFactory option of RenderOptions has been removed.

• TemplateProcessor has been removed.

• Symbols are not converted to a string before mutating DOM, so passing a Symbol to an attribute or text binding will result in an exception.

• The shady-render module has been removed and is now part of platform-support, and Lit's polyfill support now adds the following limitations: (1) Bindings in style elements are no longer supported. Previously these could not change and in the future they may be supported via static bindings. (2) ShadyCSS.styleElement is no longer called automatically. This must be called whenever dynamic changes that affect styling are made that involve css custom property shimming (older browsers) or changes to custom properties used via the deprecated @apply feature. It was previously called only on first render, and it is now up to the user to decide when this should be called. See Polyfills for more details.

• render() no longer clears the container it's rendered to. It now appends to the container by default.

• Expressions in comments are no longer rendered or updated. See Valid expression locations for more details.

• Template caching happens per callsite, not per template-tag/callsize pair. This means some rare forms of highly dynamic template tags are no longer supported.

• Arrays and other iterables passed to attribute bindings are not specially handled. Arrays will be rendered with their default toString representation. This means that html`<div class=${['a', 'b']}> will render <div class="a,b"> instead of <div class="a b">. To get the old behavior, use array.join(' ').

• Multiple bindings in a single attribute value don't require the attribute value is quoted, as long as there is no whitespace or other attribute-ending character in the attribute value. html`<div id=${a}-${b}>`

• The directive and part APIs are significantly different. See Custom Directives and the Upgrade Guide for more details.

• The Directive base class and directive() factory function are now exported from the lit-html/directive.js module.

• NodePart has been renamed to ChildPart, along with other methods and variables that use the "Node" naming, like PartType.Node which is now PartType.CHILD.

• The part exports (ChildPart, AttributePart, etc) have been change to interface-only exports. The constructors are no longer exported. Directive authors should use helpers in directive-helpers.js to construct parts.

• The eventContext render option has been changed to host.

• #2103 15a8356d - Updates the exports field of package.json files to replace the subpath folder mapping syntax with an explicit list of all exported files.

  The /-suffixed syntax for subpath folder mapping originally used in these files is deprecated. Rather than update to the new syntax, this change replaces these mappings with individual entries for all exported files so that (a) users must import using extensions and (b) bundlers or other tools that don't resolve subpath folder mapping exactly as Node.js does won't break these packages' expectations around how they're imported.

• #1764 0b4d6eda - Don't allow classMap to remove static classes. This keeps classMap consistent with building a string out of the classnames to be applied.

• Added renderBefore to render options. If specified, content is rendered before the node given via render options, e.g. {renderBefore: node}.
• Added development mode, which can be enabled by setting the development Node exports condition. See Development and production builds for more details.
• All usage of instanceof has been removed, making rendering more likely to work when multiple instances of the library interact.
• Template processing is more robust to expressions in places other than text and attribute values.
• render now returns the ChildPart that was created/updated by render.
• Added AsyncDirective, which is a Directive subclass whose disconnected callback will be called when the part containing the directive is cleared (or transitively cleared by a Part higher in the tree) or manually disconnected using the setConnected API, and whose reconnected callback will be called when manually re-connected using setConnected. When implementing disconnected, the reconnected callback should also be implemented to return the directive to a usable state. Note that LitElement will disconnect directives upon element disconnection, and re-connect directives upon element re-connection. See Async directives for more details.
• Added setConnected(isConnected: boolean) to ChildPart; when called with false, the disconnected callback will be run on any directives contained within the part (directly or transitively), but without clearing or causing a re-render to the tree. When called with true, any such directives' reconnected callback will be called prior to its next update/render callbacks. Note that LitElement will call this method by default on the rendered part in its connectedCallback and disconnectedCallback.
• Added the static-html module, a static html tag function, a literal tag function, and unsafeStatic(), which allows template authors to add strings to the static structure of the template, before it's parsed as HTML. See Static expressions for more details.
• Added lit-html/directive-helpers.js module with helpers for creating custom directives. See Custom directives for more details.
• Rendering null, undefined, or empty string in a ChildPart now has the same affect as rendering nothing: it does not produce an empty text node. When rendering into an element with Shadow DOM, this makes it harder to inadvertently prevent <slot> fallback content from rendering.
• Nested directives whose parent returns noChange are now unchanged. This allows the guard directive to guard directive values (#1519).
• Added optional creationScope to RenderOptions, which controls the node from which the template is cloned from.
• Added support for running with Trusted Types enforced.

• #1922 8189f094 - Binding noChange into an interpolated attribute expression now no longer removes the attribute on first render - instead it acts like an empty string. This is mostly noticable when using until() without a fallback in interpolated attributes.

• #1964 f43b811 - Don't publish src/ to npm.

• #2070 a48f39c8 - Throw instead of rendering an innocuous value into a style or script when security hooks are enabled.

• #2044 662209c3 - Improves disconnection handling for first-party AsyncDirectives (until, asyncAppend, asyncReplace) so that the directive (and any DOM associated with it) can be garbage collected before any promises they are awaiting resolve.

• #2098 b3121ab7 - Fix ChildPart parentNode for top-level parts to return the parentNode they will be inserted into, rather than the DocumentFragment they were cloned into. Fixes #2032.

• #2103 15a8356d - Updates the exports field of package.json files to replace the subpath folder mapping syntax with an explicit list of all exported files.

  The /-suffixed syntax for subpath folder mapping originally used in these files is deprecated. Rather than update to the new syntax, this change replaces these mappings with individual entries for all exported files so that (a) users must import using extensions and (b) bundlers or other tools that don't resolve subpath folder mapping exactly as Node.js does won't break these packages' expectations around how they're imported.

• #2074 d6b385e3 - (Cleanup) Added missing tests to close out TODOs in the code. Fixed unsafeHTML and unsafeSVG to render no content (empty string) for values undefined, null, and nothing.

• #1922 8189f094 - Binding noChange into an interpolated attribute expression now no longer removes the attribute on first render - instead it acts like an empty string. This is mostly noticable when using until() without a fallback in interpolated attributes.

• #2114 b4bd9f7c - Parts are not supported inside the template or textarea tags. In dev mode, we indicate if parts are placed here so the developer can remove them.

• #2113 5b2f3642 - Dependency upgrades including TypeScript 4.4.2

• #2072 7adfbb0c - Remove unneeded matches support in @queryAssignedNodes. Update styling tests to use static bindings where needed. Fix TODOs related to doc links.

• #2119 24feb430 - Added lit.dev/msg links to dev mode warnings.

• #1764 0b4d6eda - Don't allow classMap to remove static classes. This keeps classMap consistent with building a string out of the classnames to be applied.

• #2071 01353317 - In dev mode, throw for tag name bindings. These should use static templates.

• #2070 a48f39c8 - Throw instead of rendering an innocuous value into a style or script when security hooks are enabled.

• #2075 724a9aab - Ensures dev mode warnings do not spam by taking care to issue unique warnings only once.

• #2076 0d703bfb - Optimize setting primitives on ChildNode.

• #2073 0312f3e5 - (Cleanup) Removed obsolete TODOs from codebase

• #2056 e5667d66 - Fixed issue where AsyncDirectives could see this.isConnected === true if a LitElement performed its initial render while it was disconnected.

• #2128 cc5c3a09 - Add test for AsyncDirectives that synchronously call this.setValue()

• #2046 043a16fb - In development mode, constructing an EventPart from an improperly formed attribute will now throw: the attribute must contain only a single expression and the surrounding two strings must be the empty string. Before, constructing an EventPart with extra expressions or surrounding text would cause that part to be silently and incorrectly treated as an AttributePart.

• #2043 761375ac - Update some internal types to avoid casting globalThis to any to retrieve globals where possible.

• #1959 69389958 - Changed all prefixes used for minifying object and class properties from greek characters to ASCII, to avoid requiring an explicit script charset on some browser/webview environments.

• #2002 ff0d1556 - Fixes polyfill-support styling issues: styling should be fully applied by firstUpdated/update time; late added styles are now retained (matching Lit1 behavior)

• #2034 5768cc60 - Reverts the change in Lit 2 to pause ReactiveElement's update cycle while the element is disconnected. The update cycle for elements will now run while disconnected as in Lit 1, however AsyncDirectives must now check the this.isConnected flag during update to ensure that e.g. subscriptions that could lead to memory leaks are not made when AsyncDirectives update while disconnected.

• #1942 c8fe1d4 - For minified class fields on classes in lit libraries, added prefix to stable properties to avoid collisions with user properties.

• #2041 52a47c7e - Remove some unnecessary internal type declarations.

• #1959 6938995 - Changed prefix used for minifying class field names on lit libraries to stay within ASCII subset, to avoid needing to explicitly set the charset for scripts in some browsers.

• #1937 3663f09 - Re-export PropertyPart from 'directive.ts'

• #1964 f43b811 - Don't publish src/ to npm.

• #1991 f05be301 - Fixed bug where Template.createElement was not patchable by polyfill-support when compiled using closure compiler, leading to incorrect style scoping.

• #2016 e6dc6a7 - Clean up internal TypeScript types

• #1990 56e8efd3 - Fixed an error thrown when an empty <style></style> tag is rendered while using the @apply shim under native Shadow DOM.

• #2044 662209c3 - Improves disconnection handling for first-party AsyncDirectives (until, asyncAppend, asyncReplace) so that the directive (and any DOM associated with it) can be garbage collected before any promises they are awaiting resolve.

• #1972 a791514b - Properties that must remain unminified are now compatible with build tools other than rollup/terser.

• #2050 8758e06 - Fix syntax highlighting in some documentation examples

Changes below were based on the Keep a Changelog format. All changes above are generated automatically by Changesets.

• Exported the Ref interface.

• Add dependency on trustedtypes typings.

• Added defer-hydration attribute handling to experimental-hydrate, which helps coordinate ordered wakeup of custom elements during hydration.
• Added support for running with Trusted Types enforced.

• (Since 2.0.0-pre.7) Renamed hydrate module to experimental-hydrate to reflect its experimental nature. Experimental modules may undergo breaking changes within otherwise non-major releases.

• Added optional creationScope to RenderOptions, which controls the node from which the template is cloned from.
• (Since 2.0.0-pre.6) Reintroduced the SVGTemplateResult type. (#1623)

• @apply now functions correctly under native Shadow DOM when template parts are used. (#1739).

• styleMap() now removes properties if the value is set to undefined or null, as opposed to not being a property of the style object. (#1665).

• (Since 2.0.0-pre.4) Added asyncappend and asyncReplace directives.

• Nested directives whose parent returns noChange are now unchanged. This allows the guard directive to guard directive values (#1519).

• (Since 2.0.0-pre.4) Removes second klass argument from isDirectiveResult since it is generally not version-agnostic to test directives using instanceof. A new getDirectiveClass helper is introduced, which allows for directive class branding checks instead.
• (Since 2.0.0-pre.4) DisconnectableDirective was renamed to AsyncDirective, and its module name was renamed from disconnectable-directive to async-directive.
• (Since 2.0.0-pre.4) Rendering null, undefined, or empty string in a ChildPart now has the same affect as rendering nothing: it does not produce an empty text node. When rendering into an element with Shadow DOM, this makes it harder to inadvertently prevent <slot> fallback content from rendering.
• (Since 2.0.0-pre.4) DisconnectableDirective's disconnectedCallback and reconnectedCallback were renamed to disconnected and reconnected.
• (Since 2.0.0-pre.4) Renamed platform-support to polyfill-support.

• render now returns the NodePart that was created/updated by render.

• Added DisconnectableDirective, which is a Directive subclass whose disconnectedCallback will be called when the part containing the directive is cleared (or transitively cleared by a Part higher in the tree) or manually disconnected using the setConnected API, and whose reconnectedCallback will be called when manually re-connected using setConnected. When implementing disconnectedCallback, reconnectedCallback should also be implemented to return the directive to a usable state. Note that LitElement will disconnect directives upon element disconnection, and re-connect directives upon element re-connection.

• Added setConnected(isConnected: boolean) to NodePart; when called with false, disconnectedCallback will be run on any directives contained within the part (directly or transitively), but without clearing or causing a re-render to the tree. When called with true, any such directives' reconnectedCallback will be called prior to its next update/render callbacks. Note that LitElement will call this method by default on the rendered part in its connectedCallback and disconnectedCallback.

• Added unsafeStatic(), which allows template authors to add strings to the static structure of the template, before it's parsed as HTML.

• Added isPrimitive(), isTemplateResult(), and isDirectiveResult() to lit-html/directive-helpers.js.

• Directives that asynchronously update their part value must now extend DisconnectableDirective and call this.setValue(), a new API exposed on the DisconnectableDirective class. Directives that render synchronously to their update lifecycle should simply return the value to be committed to their part from update/render.

• The Directive base class and directive() factory function are now exported from the lit-html/directive.js module.

• (since 2.0.0-pre.3) The Part type constants (NODE_PART, etc) are removed from the main lit-html module and exported as an enum-object named PartType from lit-html/directive.js. Use PartType.NODE instead of NODE_TYPE.

• (since 2.0.0-pre.3)) lit-html/parts.js has been renamed to lit-html/directive-helpers.js.

• (since 2.0.0-pre.3)) Originally in lit-html/parts.js, createAndInsertPart() and insertPartBefore() have been combined into a single insertPart() function in lit-html/directive-helpers.js. detachNodePart() and restoreNodePart() have been removed in favor of moving parts with insertPart().

• (since 2.0.0-pre.3) NodePart has been renamed to ChildPart, along with other methods and variables that use the "Node" naming, like PartType.Node which is now PartType.CHILD.

• (since 2.0.0-pre.3) The DirectiveClass, DirectiveParameters and PartInfo types have been moved from lit-html to lit-html/directive.ts.

• (since 2.0.0-pre.3) The part exports (ChildPart, AttributePart, etc) have been change to interface-only exports. The constructors are no longer exported. Directive authors should use helpers in directive-helpers.js to construct parts.

• (since 2.0.0-pre.3) The setPartValue function in directive-helpers.js has been renamed to setChildPartValue and now only supports ChildParts. Directives that require updating their container part outside the render/update lifecycle should extend DisconnectableDirective and use this.setValue().

• (since 2.0.0-pre.3) The eventContext render option has been changed to host.

• The shady-render module has been removed and is now part of platform-support. There are also a couple of breaking changes. (1) Bindings in style elements are no longer supported. Previously these could not change and in the future they may be supported via static bindings. (2) ShadyCSS.styleElement is no longer called automatically. This must be called whenever dynamic changes that affect styling are made that involve css custom property shimming (older browsers) or changes to custom properties used via the deprecated @apply feature. It was previously called only on first render, and it is now up to the user to decide when this should be called.
• render() no longer clears the container it's rendered to. It now appends to the container by default.
• Expressions in comments are not rendered or updated.
• Template caching happens per callsite, not per template-tag/callsize pair. This means some rare forms of highly dynamic template tags are no longer supported.
• Arrays and other iterables passed to attribute bindings are not specially handled. Arrays will be rendered with their default toString representation. This means that html`<div class=${['a', 'b']}> will render <div class="a,b"> instead of <div class="a b">. To get the old behavior, use array.join(' ').
• Multiple bindings in a single attribute value don't require the attribute value is quoted, as long as there is no whitespace or other attribute-ending character in the attribute value. html`<div id=${a}-${b}>
• The directive and part APIs are significantly different. See the README for more details.

• Added renderBefore to render options. If specified, content is rendered before the node given via render options, e.g. {renderBefore: node}.
• Added development mode, which can be enabled by setting the development Node exports condition. See README.md for more details.

• All usage of instanceof has been removed, making rendering more likely to work when multiple instances of the library interact.
• Template processing is more robust to expressions in places other than text and attribute values.

• The templateFactory option of RenderOptions has been removed.
• TemplateProcessor has been removed.
• Symbols are not converted to a string before mutating DOM, so passing a Symbol to an attribute or text binding will result in an exception.
• The asyncAppend and asyncReplace directives are not implemented.

• Set the "type" field in package.json to "module. (#1146)

• Added support for Trusted Types. This support uses a policy named 'lit-html' for parsing the static parts of html literals, and ensures that we pass trusted type values through to the DOM when used in bindings. (#1153)
• Export the shadyTemplateFactory from lib/shady-render.js (#1135)

• Added TypeScript type declarations for older versions of TypeScript. We're currently testing back to TS 3.4. We can't commit to never breaking TypeScript builds, but we'll be supporting older versions as best we can.

• Added unsafeSVG directive to bind SVG source inside SVGs. (#304)
• Added templateContent() directive for stamping out the contents of an HTML template into a text binding. (#1058)
• Added the live() directive. (#877)

• Fixed a bug where classMap and styleMap directives wouldn't render mutated objects. (#972)
• Fixed a bug where ifDefined() would set an attribute even when the value didn't change. (#890)
• Change classMap directive to set classes correctly on SVGs (#1070).

• Fixed a bug where bindings in comments could be written as text in some cases. (#926)

• render and shady-render now both accept any value that is renderable by NodePart. (#910)

• Many small performance enhancements.
• Private names are now named with a __ prefix (#859).

• Setup continuous benchmarking with Tachometer (#887).

• Prevent empty styles from causing exceptions or breaking rendering when using shady-render (#760).
• Primitive values in attributes are now always simply stringified, regardless of whether they are iterable. (#830)
• Adopt and upgrade template fragments after processing for parts (#831).
• Fixed bindings with attribute-like expressions preceeding them (#855).
• Fixed errors with bindings in HTML comments (#882).

• Tons of docs updates (#746), (#675), (#724), (#753), (#764), (#763), (#765), (#767), (#768), (#734), (#771), (#766), (#773), (#770), (#769), (#777), (#776), (#754), (#779)

• Global version of lit-html on window (#790).

• Removed use of any outside of test code (#741).

• Performance improvements to template processing. (#690)

• Added the nothing sentinel value which can be used to clear a part. (#673)

• Fixed #702: a bug with the unsafeHTML directive when changing between unsafe and other values. (#703)
• Fixed #708: a bug with the until directive where placeholders could overwrite resolved Promises. (#721)

• Documentation updates.
• Fixed typing for template_polyfill createElement call.

• until() can now take any number of sync or async arguments. (#555)
• guard() supports multiple dependencies. If the first argument to guard() is an array, the array items are checked for equality to previous values. (#666)
• Renamed classMap.js and styleMap.js files to kebab-case. (#644)

• Added cache() directive. (#646)
• Removed Promise as a supposed node-position value type. (#555)
• Added a minimal <template> polyfill.

• Removed the when() directive. Users may achieve similar behavior by wrapping a ternary with the cache() directive.

• Bound attribute names are rewritten to avoid IE/Edge removing SVG and style attributes. (#640)
• Ensure shady-render prepares styling for a scope before attaching child elements. (#664)
• Handle CSS Custom Variables in the styleMap directive. #642)

• Directives are now defined by passing the entire directive factory function to directive(). (#562)

• Fix issue on obscure browsers that do not accept event listener objects by using callback as event part listener (#581)
• Fix KeyFn and ItemTemplate types (#570)
• Don't use export * to workaround rollup bug (#556)
• eventContext is no longer used as the this value for event listener objects (object with a handleEvent method), as the object itself is supposed to be the this value. (#576)

• Re-implemented repeat directive for better performance (#501)
• Updated TypeScript dependency to 3.1
• render() now takes an options object as the third argument. (#523)

• Event listeners are called with a configurable this reference, which is set via the eventContext option to render(). (#523)
• Support for event listener options, by passing the listener itself as both the second and third arguments to add/removeEventListener().

• Fixed issues with shady-render introduced in 0.11.3 (#504 and #505).

• Moved upgrading of custom elements in template fragments to a common location in TemplateInstance (#489)
• Rewrite render() to reuse the logic in NodePart. render() now supports all the data types that NodeParts do. (#491)

• Fixed bug when using the ShadyCSS @apply` shim. (#502)

• Added classMap and styleMap directives (#486)

• Fixed bug in asyncReplace when rerendering the same iterable (#485)
• Update properties before upgrading custom elements (#455)
• Cache the ShadyCSS version lookup (#477)

• Eliminated a cycle in the module import graph (#472)
• Remove the default value for the templateProcessor parameter in TemplateResult#constuctor, making it a required parameter (#472)

• Added support for property, event, and boolean bindings to default syntax (#398)
• Added guard directive (#438)
• Added when directive (#439)

• Split implementation into multiple small modules and merged lit-html.js and core.js (#436)
• Moved directives into top-level directives/ directory (#436)
• Replaced PartCallback with TemplateProcessor (#405)
• Unified NodePart and AttributePart interfaces (#400)
  • AttributePart#setValue() takes a single value
  • Part has separate setValue() and commit() phases
  • Added AttributeCommitter to commit attribute values once for multiple AttributeParts

• Removed lit-extended.js (#436)

• Render initial undefined values in attributes (#377)
• Handle case-sensitive attributes like viewBox correctly (#376)
• Support bindings in <template> elements (#343)
• Don’t break templates when HTML comments have bindings in them (#446)
• IE: Don't use Set() constructor arguments (#401)
• Handle forms as Node instead of iterable (#404)
• Update values after upgrading custom elements (#385)
• Dirty check primitive values passed to unsafeHTML() (#384)
• Handle forms as Node instead of iterable (#404)
• Upgrade disconnected custom elements before setting properties on them. (#442)
• Fix style attribute bindings in IE (#448)

• Added noChange - Value in favour of directiveValue (deprecated).
  • A noChange - Value signals that a value was handled by a directive and should not be written to the DOM
• Updated shady-render to render styles in order, work with @apply, and work in browers where CSS Custom Properties must be polyfilled, like IE 11.
• Introduced API to modify template contents safely without breaking template parts
  • insertNodeIntoTemplate(template: Template, node: Node, refNode: Node|null)
  • removeNodesFromTemplate(template: Template, nodesToRemove: Set<Node>)

• Added IE11 support
• Declarative events in lit-extended are more efficient when handlers change

• Refactored how template tags and render() are implemented so that all specialization of template syntax is done in tags, not render(), allowing for the mixing-in of templates of different syntaxes, and for hooks in render() to change templates before they're initially processed.
• Added ShadyCSS support in lib/shady-render.js. It's exported render function will pass templates to ShadyCSS's prepareTemplate() function to process style tags and elements in the template for emulate CSS scoping.
• lit-extended: Attribute bindings with a ? suffix on the name now act as boolean attributes. The attribute will be removed for falsey values and set to '' for truthy values, matching the HTML specification behavior for boolean attributes.
• Fixed a bug where directives rendered incorrectly on AttributeParts and PropertyParts

• Allow all valid HTML attribute names, including emoji and Angular-style (foo)= and [foo]= names.
• Drastically improved performance of the repeat directive.
• Fixed an issue with expressions directly following elements.
• Fixed numerous bugs with the repeat directive.
• Performance improvements for template setup
• Internal code cleanup
• Support synchronous thenables
• Added the asyncAppend and asyncReplace directives to handle async iterable values in expressions.

• Added the svg template tag for creating partial SVG content
• Support for expressions inside tables and other elements with limited permitted content
• Only remove whitespace between elements, or at the start or end of elements
• Fixed bugs with rendering iterables
• A few IE/Edge fixes. Closer to full support.

• Fixed removing event handlers when setting them to undefined.
• Allow the text "{{}}" to appear in templates.
• Optimized clearing of Parts.
• Added unsafeHTML() directive to bind values as HTML source.
• Optimizations, simplification and bug fixes of Array handling code.
• Update to extension API: added partCallback parameter to render().
• Added the directive() decorator function to create directives. Functions values are no longer treated as directive by default, simplifying declarative event handlers.