Perf improvements v2 (preactjs#278)

* more perf improvements

* remove

* undo loop change

* put self closing in a set

* inline

* remove cross

* add missing void el

* create non-dimensional cahce

* last bits

* Create thick-islands-share.md

Author: JoviDeCroock

.changeset/thick-islands-share.md

@@ -0,0 +1,10 @@
+---
+"preact-render-to-string": patch
+---
+
+Improve performance by
+
+- storing the void_elements in a Set
+- hoisting the `x-link` regex
+- remove case-insensitive from regexes and calling `.toLowerCase()` instead
+- caching suffixes for css-props

package-lock.json

@@ -47,7 +47,13 @@ export default function renderToString(vnode, context) {
 	parent[CHILDREN] = [vnode];
 
 	try {
-		return _renderToString(vnode, context || {}, false, undefined, parent);
+		return _renderToString(
+			vnode,
+			context || EMPTY_OBJ,
+			false,
+			undefined,
+			parent
+		);
 	} finally {
 		// options._commit, we don't schedule any effects in this library right now,
 		// so we can pass an empty queue to this hook.
@@ -62,6 +68,8 @@ function markAsDirty() {
 	this.__d = true;
 }
 
+const EMPTY_OBJ = {};
+
 /**
  * @param {VNode} vnode
  * @param {Record<string, unknown>} context
@@ -79,7 +87,7 @@ function renderClassComponent(vnode, context) {
 	// turn off stateful re-rendering:
 	c[DIRTY] = true;
 
-	if (c.state == null) c.state = {};
+	if (c.state == null) c.state = EMPTY_OBJ;
 
 	if (c[NEXT_STATE] == null) {
 		c[NEXT_STATE] = c.state;
@@ -163,8 +171,7 @@ function _renderToString(vnode, context, isSvgMode, selectValue, parent) {
 		component;
 
 	// Invoke rendering on Components
-	let isComponent = typeof type === 'function';
-	if (isComponent) {
+	if (typeof type === 'function') {
 		if (type === Fragment) {
 			rendered = props.children;
 		} else {
@@ -307,15 +314,16 @@ function _renderToString(vnode, context, isSvgMode, selectValue, parent) {
 				}
 				break;
 
-			default:
+			default: {
 				if (isSvgMode && XLINK.test(name)) {
-					name = name.toLowerCase().replace(/^xlink:?/, 'xlink:');
+					name = name.toLowerCase().replace(XLINK_REPLACE_REGEX, 'xlink:');
 				} else if (UNSAFE_NAME.test(name)) {
 					continue;
 				} else if (name[0] === 'a' && name[1] === 'r' && v != null) {
 					// serialize boolean aria-xyz attribute values as strings
 					v += '';
 				}
+			}
 		}
 
 		// write this attribute to the buffer
@@ -349,25 +357,29 @@ function _renderToString(vnode, context, isSvgMode, selectValue, parent) {
 	if (options.unmount) options.unmount(vnode);
 
 	// Emit self-closing tag for empty void elements:
-	if (!html) {
-		switch (type) {
-			case 'area':
-			case 'base':
-			case 'br':
-			case 'col':
-			case 'embed':
-			case 'hr':
-			case 'img':
-			case 'input':
-			case 'link':
-			case 'meta':
-			case 'param':
-			case 'source':
-			case 'track':
-			case 'wbr':
-				return s + ' />';
-		}
+	if (!html && SELF_CLOSING.has(type)) {
+		return s + ' />';
 	}
 
 	return s + '>' + html + '</' + type + '>';
 }
+
+const XLINK_REPLACE_REGEX = /^xlink:?/;
+const SELF_CLOSING = new Set([
+	'area',
+	'base',
+	'br',
+	'col',
+	'command',
+	'embed',
+	'hr',
+	'img',
+	'input',
+	'keygen',
+	'link',
+	'meta',
+	'param',
+	'source',
+	'track',
+	'wbr'
+]);

src/index.js

@@ -1,9 +1,9 @@
-// DOM properties that should NOT have "px" added when numeric
-export const IS_NON_DIMENSIONAL = /acit|ex(?:s|g|n|p|$)|rph|grid|ows|mnc|ntw|ine[ch]|zoo|^ord|^--/i;
 export const VOID_ELEMENTS = /^(?:area|base|br|col|embed|hr|img|input|link|meta|param|source|track|wbr)$/;
 export const UNSAFE_NAME = /[\s\n\\/='"\0<>]/;
 export const XLINK = /^xlink:?./;
 
+// DOM properties that should NOT have "px" added when numeric
+const IS_NON_DIMENSIONAL = /acit|ex(?:s|g|n|p|$)|rph|grid|ows|mnc|ntw|ine[ch]|zoo|^ord|^--/;
 const ENCODED_ENTITIES = /["&<]/;
 
 /** @param {string} str */
@@ -50,6 +50,7 @@ export let isLargeString = (s, length, ignoreLines) =>
 	String(s).indexOf('<') !== -1;
 
 const JS_TO_CSS = {};
+const SUFFIX_CACHE = {};
 
 const CSS_REGEX = /([A-Z])/g;
 // Convert an Object style to a CSSText string
@@ -64,14 +65,17 @@ export function styleObjToCss(s) {
 					: JS_TO_CSS[prop] ||
 					  (JS_TO_CSS[prop] = prop.replace(CSS_REGEX, '-$1').toLowerCase());
 
-			str =
-				str +
-				name +
-				':' +
-				val +
-				(typeof val === 'number' && IS_NON_DIMENSIONAL.test(prop) === false
-					? 'px;'
-					: ';');
+			let suffix = ';';
+			if (SUFFIX_CACHE[name]) {
+				suffix = 'px';
+			} else if (
+				typeof val === 'number' &&
+				IS_NON_DIMENSIONAL.test(prop.toLowerCase()) === false
+			) {
+				SUFFIX_CACHE[name] = true;
+				suffix = 'px';
+			}
+			str = str + name + ':' + val + suffix;
 		}
 	}
 	return str || undefined;