Add support for passing styles as CSS fields

Previously, all style props were passed using DOM (`backgroundColor`)
casing.
This does not work in some any other JSX runtimes.
Instead, some JSX runtimes want `background-color` instead.

This adds an option for that.

This commit also fixes support for CSS custom properties (`--fg: red`),
which always have to include those initial dashes, even when setting to
the DOM.

Author: wooorm

Diff for: index.js

@@ -8,6 +8,7 @@
  * @typedef {import('./lib/index.js').Props} Props
  * @typedef {import('./lib/index.js').Source} Source
  * @typedef {import('./lib/index.js').Space} Space
+ * @typedef {import('./lib/index.js').StylePropertyNameCase} StylePropertyNameCase
  */
 
 export {toJsxRuntime} from './lib/index.js'

Diff for: lib/index.js

@@ -46,11 +46,17 @@
  * @typedef {'html' | 'svg'} Space
  *   Namespace.
  *
- * @typedef {'react' | 'html'} ElementAttributeNameCase
- *   Specify casing to use for attribute names.
+ * @typedef {'html' | 'react'} ElementAttributeNameCase
+ *   Casing to use for attribute names.
  *
- *   React casing is for example `className`, `strokeLinecap`, `xmlLang`.
  *   HTML casing is for example `class`, `stroke-linecap`, `xml:lang`.
+ *   React casing is for example `className`, `strokeLinecap`, `xmlLang`.
+ *
+ * @typedef {'css' | 'dom'} StylePropertyNameCase
+ *   Casing to use for property names in `style` objects.
+ *
+ *   CSS casing is for example `background-color` and `-webkit-line-clamp`.
+ *   DOM casing is for example `backgroundColor` and `WebkitLineClamp`.
  *
  * @typedef Source
  *   Info about source.
@@ -99,6 +105,8 @@
  *   Pass `node` to components.
  * @property {ElementAttributeNameCase} elementAttributeNameCase
  *   Casing to use for attribute names.
+ * @property {StylePropertyNameCase} stylePropertyNameCase
+ *   Casing to use for property names in `style` objects.
  * @property {Schema} schema
  *   Current schema.
  * @property {unknown} Fragment
@@ -122,6 +130,8 @@
  *   Pass the hast element node to components.
  * @property {ElementAttributeNameCase | null | undefined} [elementAttributeNameCase='react']
  *   Specify casing to use for attribute names.
+ * @property {StylePropertyNameCase | null | undefined} [stylePropertyNameCase='dom']
+ *   Specify casing to use for property names in `style` objects.
  * @property {Space | null | undefined} [space='html']
  *   Whether `tree` is in the `'html'` or `'svg'` space.
  *
@@ -195,6 +205,9 @@ import {whitespace} from 'hast-util-whitespace'
 
 const own = {}.hasOwnProperty
 
+const cap = /[A-Z]/g
+const dashSomething = /-([a-z])/g
+
 // `react-dom` triggers a warning for *any* white space in tables.
 // To follow GFM, `mdast-util-to-hast` injects line endings between elements.
 // Other tools might do so too, but they don’t do here, so we remove all of
@@ -255,6 +268,7 @@ export function toJsxRuntime(tree, options) {
     schema: options.space === 'svg' ? svg : html,
     passNode: options.passNode || false,
     elementAttributeNameCase: options.elementAttributeNameCase || 'react',
+    stylePropertyNameCase: options.stylePropertyNameCase || 'dom',
     components: options.components || {},
     filePath,
     create
@@ -485,8 +499,15 @@ function createProperty(state, node, prop, value) {
   }
 
   // React only accepts `style` as object.
-  if (info.property === 'style' && typeof value === 'string') {
-    return ['style', parseStyle(state, node, value)]
+  if (info.property === 'style') {
+    let styleObject =
+      typeof value === 'object' ? value : parseStyle(state, node, String(value))
+
+    if (state.stylePropertyNameCase === 'css') {
+      styleObject = transformStyleToCssCasing(styleObject)
+    }
+
+    return ['style', styleObject]
   }
 
   return [
@@ -534,8 +555,8 @@ function parseStyle(state, node, value) {
   return result
 
   /**
-   * Add a CSS property (normal, so with dashes) to `result` as a camelcased
-   * CSS property.
+   * Add a CSS property (normal, so with dashes) to `result` as a DOM CSS
+   * property.
    *
    * @param {string} name
    *   Key.
@@ -545,9 +566,39 @@ function parseStyle(state, node, value) {
    *   Nothing.
    */
   function replacer(name, value) {
-    if (name.slice(0, 4) === '-ms-') name = 'ms-' + name.slice(4)
-    result[name.replace(/-([a-z])/g, replace)] = value
+    let key = name
+
+    if (key.slice(0, 2) !== '--') {
+      if (key.slice(0, 4) === '-ms-') key = 'ms-' + key.slice(4)
+      key = key.replace(dashSomething, toCamel)
+    }
+
+    result[key] = value
+  }
+}
+
+/**
+ * Transform a DOM casing style object to a CSS casing style object.
+ *
+ * @param {Style} domCasing
+ * @returns {Style}
+ */
+function transformStyleToCssCasing(domCasing) {
+  /** @type {Style} */
+  const cssCasing = {}
+  /** @type {string} */
+  let from
+
+  for (from in domCasing) {
+    if (own.call(domCasing, from)) {
+      let to = from.replace(cap, toDash)
+      // Handle `ms-xxx` -> `-ms-xxx`.
+      if (to.slice(0, 3) === 'ms-') to = '-' + to
+      cssCasing[to] = domCasing[from]
+    }
   }
+
+  return cssCasing
 }
 
 /**
@@ -560,6 +611,18 @@ function parseStyle(state, node, value) {
  * @returns {string}
  *   Capitalized `$1`.
  */
-function replace(_, $1) {
+function toCamel(_, $1) {
   return $1.toUpperCase()
 }
+
+/**
+ * Make `$0` dash cased.
+ *
+ * @param {string} $0
+ *   Capitalized ASCII leter.
+ * @returns {string}
+ *   Dash and lower letter.
+ */
+function toDash($0) {
+  return '-' + $0.toLowerCase()
+}

Diff for: readme.md

@@ -28,6 +28,7 @@ with an automatic JSX runtime.
     *   [`Props`](#props)
     *   [`Source`](#source)
     *   [`Space`](#space-1)
+    *   [`StylePropertyNameCase`](#stylepropertynamecase-1)
 *   [Examples](#examples)
     *   [Example: Preact](#example-preact)
     *   [Example: Vue](#example-vue)
@@ -157,19 +158,19 @@ Components to use ([`Partial<Components>`][api-components], optional).
 Each key is the name of an HTML (or SVG) element to override.
 The value is the component to render instead.
 
+###### `elementAttributeNameCase`
+
+Specify casing to use for attribute names
+([`ElementAttributeNameCase`][api-element-attribute-name-case], default:
+`'react'`).
+
 ###### `filePath`
 
 File path to the original source file (`string`, optional).
 
 Passed in source info to `jsxDEV` when using the automatic runtime with
 `development: true`.
 
-###### `elementAttributeNameCase`
-
-Specify casing to use for attribute names
-([`ElementAttributeNameCase`][api-element-attribute-name-case], default:
-`'react'`).
-
 ###### `passNode`
 
 Pass the hast element node to components (`boolean`, default: `false`).
@@ -189,6 +190,12 @@ it.
 > Passing SVG might break but fragments of modern SVG should be fine.
 > Use `xast` if you need to support SVG as XML.
 
+###### `stylePropertyNameCase`
+
+Specify casing to use for property names in `style` objects
+([`StylePropertyNameCase`][api-style-property-name-case], default:
+`'dom'`).
+
 ### `Components`
 
 Possible components to use (TypeScript type).
@@ -222,10 +229,10 @@ type Component<ComponentProps> =
 
 ### `ElementAttributeNameCase`
 
-Specify casing to use for attribute names (TypeScript type).
+Casing to use for attribute names (TypeScript type).
 
-React casing is for example `className`, `strokeLinecap`, `xmlLang`.
 HTML casing is for example `class`, `stroke-linecap`, `xml:lang`.
+React casing is for example `className`, `strokeLinecap`, `xmlLang`.
 
 ###### Type
 
@@ -329,6 +336,19 @@ Namespace (TypeScript type).
 type Space = 'html' | 'svg'
 ```
 
+### `StylePropertyNameCase`
+
+Casing to use for property names in `style` objects (TypeScript type).
+
+CSS casing is for example `background-color` and `-webkit-line-clamp`.
+DOM casing is for example `backgroundColor` and `WebkitLineClamp`.
+
+###### Type
+
+```ts
+type StylePropertyNameCase = 'dom' | 'css'
+```
+
 ## Examples
 
 ### Example: Preact
@@ -420,7 +440,8 @@ It exports the additional types [`Components`][api-components],
 [`ElementAttributeNameCase`][api-element-attribute-name-case],
 [`Fragment`][api-fragment], [`Jsx`][api-jsx], [`JsxDev`][api-jsx-dev],
 [`Options`][api-options], [`Props`][api-props], [`Source`][api-source],
-and [`Space`][api-Space].
+[`Space`][api-Space],
+and [`StylePropertyNameCase`][api-style-property-name-case].
 
 The function `toJsxRuntime` returns a `JSX.Element`, which means that the JSX
 namespace has to by typed.
@@ -537,3 +558,5 @@ abide by its terms.
 [api-source]: #source
 
 [api-space]: #space-1
+
+[api-style-property-name-case]: #stylepropertynamecase-1

Diff for: test/index.js

@@ -182,6 +182,83 @@ test('properties', () => {
     'should support `style`'
   )
 
+  assert.equal(
+    renderToStaticMarkup(
+      toJsxRuntime(
+        {
+          type: 'element',
+          tagName: 'div',
+          // @ts-expect-error: style as object, normally not supported, but passed through here.
+          properties: {style: {color: 'red'}},
+          children: []
+        },
+        production
+      )
+    ),
+    '<div style="color:red"></div>',
+    'should support `style` as an object'
+  )
+
+  assert.equal(
+    renderToStaticMarkup(
+      toJsxRuntime(
+        h('div', {style: '-webkit-transform: rotate(0.01turn)'}),
+        production
+      )
+    ),
+    '<div style="-webkit-transform:rotate(0.01turn)"></div>',
+    'should support vendor prefixes'
+  )
+
+  assert.equal(
+    renderToStaticMarkup(
+      toJsxRuntime(
+        h('div', {style: '--fg: #0366d6; color: var(--fg)'}),
+        production
+      )
+    ),
+    '<div style="--fg:#0366d6;color:var(--fg)"></div>',
+    'should support CSS variables'
+  )
+
+  /** @type {unknown} */
+  let foundProps
+
+  assert.equal(
+    renderToStaticMarkup(
+      toJsxRuntime(
+        h('div', {
+          style:
+            '-webkit-transform:rotate(0.01turn); --fg: #0366d6; color: var(--fg); -ms-transition: unset'
+        }),
+        {
+          ...production,
+          jsx(type, props) {
+            foundProps = props
+            return production.jsx('div', {children: []}, undefined)
+          },
+          stylePropertyNameCase: 'css'
+        }
+      )
+    ),
+    '<div></div>',
+    'should support CSS cased style objects (1)'
+  )
+
+  assert.deepEqual(
+    foundProps,
+    {
+      children: undefined,
+      style: {
+        '-webkit-transform': 'rotate(0.01turn)',
+        '--fg': '#0366d6',
+        color: 'var(--fg)',
+        '-ms-transition': 'unset'
+      }
+    },
+    'should support CSS cased style objects (2)'
+  )
+
   assert.throws(
     () => {
       toJsxRuntime(h('div', {style: 'color:red; /*'}), production)