[fix] low-level performance tuning

createDOMProps: avoid using default parameters as Babel compiles the
function to calls using 'arguments', which Chrome flags as a deopt.
Replace 'typeof' calls with slightly faster calls to constructor.

onLayout: batch layout measurements in a single requestAnimationFrame.

Close #490

src/apis/UIManager/index.js

@@ -1,4 +1,5 @@
 import requestAnimationFrame from 'fbjs/lib/requestAnimationFrame';
+import setImmediate from 'fbjs/lib/setImmediate';
 import setValueForStyles from '../../vendor/setValueForStyles';
 
 const getRect = node => {
@@ -14,9 +15,14 @@ const getRect = node => {
   return { height, left, top, width };
 };
 
-const measureLayout = (node, relativeToNativeNode, callback) => {
-  requestAnimationFrame(() => {
+let hasRequestedAnimationFrame = false;
+const measureLayoutQueue = [];
+
+const processLayoutQueue = () => {
+  measureLayoutQueue.splice(0, 250).forEach((item) => {
+    const [node, relativeToNativeNode, callback] = item;
     const relativeNode = relativeToNativeNode || (node && node.parentNode);
+
     if (node && relativeNode) {
       const relativeRect = getRect(relativeNode);
       const { height, left, top, width } = getRect(node);
@@ -24,7 +30,23 @@ const measureLayout = (node, relativeToNativeNode, callback) => {
       const y = top - relativeRect.top;
       callback(x, y, width, height, left, top);
     }
-  });
+  })
+
+  if (measureLayoutQueue.length > 0) {
+    setImmediate(processLayoutQueue);
+  }
+}
+
+const measureLayout = (node, relativeToNativeNode, callback) => {
+  if (!hasRequestedAnimationFrame) {
+    requestAnimationFrame(() => {
+      hasRequestedAnimationFrame = false;
+      processLayoutQueue();
+    });
+  }
+
+  hasRequestedAnimationFrame = true;
+  measureLayoutQueue.push([node, relativeToNativeNode, callback]);
 };
 
 const UIManager = {

src/modules/createDOMElement/index.js

@@ -44,14 +44,12 @@ const createDOMElement = (component, props) => {
 
   // normalize DOM events to match React Native events
   // TODO: move this out of the render path
-  for (const prop in domProps) {
-    if (Object.prototype.hasOwnProperty.call(domProps, prop)) {
-      const isEventHandler = typeof prop === 'function' && eventHandlerNames[prop];
-      if (isEventHandler) {
-        domProps[prop] = wrapEventHandler(prop);
-      }
+  Object.keys(domProps).forEach((prop) => {
+    const isEventHandler = typeof prop === 'function' && eventHandlerNames[prop];
+    if (isEventHandler) {
+      domProps[prop] = wrapEventHandler(prop);
     }
-  }
+  });
 
   return <Component {...domProps} />;
 };

src/modules/createDOMProps/index.js

@@ -39,7 +39,11 @@ const pointerEventStyles = StyleSheet.create({
 
 const resolver = style => StyleRegistry.resolve(style);
 
-const createDOMProps = (rnProps, resolveStyle = resolver) => {
+const createDOMProps = (rnProps, resolveStyle) => {
+  if (!resolveStyle) {
+    resolveStyle = resolver;
+  }
+
   const props = rnProps || emptyObject;
   const {
     accessibilityLabel,
@@ -72,19 +76,19 @@ const createDOMProps = (rnProps, resolveStyle = resolver) => {
   if (accessible === true) {
     domProps.tabIndex = AccessibilityUtil.propsToTabIndex(props);
   }
-  if (typeof accessibilityLabel === 'string') {
+  if (accessibilityLabel && accessibilityLabel.constructor === String) {
     domProps['aria-label'] = accessibilityLabel;
   }
-  if (typeof accessibilityLiveRegion === 'string') {
+  if (accessibilityLiveRegion && accessibilityLiveRegion.constructor === String) {
     domProps['aria-live'] = accessibilityLiveRegion === 'none' ? 'off' : accessibilityLiveRegion;
   }
-  if (typeof className === 'string' && className !== '') {
+  if (className && className.constructor === String) {
     domProps.className = domProps.className ? `${domProps.className} ${className}` : className;
   }
   if (importantForAccessibility === 'no-hide-descendants') {
     domProps['aria-hidden'] = true;
   }
-  if (typeof role === 'string') {
+  if (role && role.constructor === String) {
     domProps.role = role;
     if (role === 'button') {
       domProps.type = 'button';
@@ -92,13 +96,13 @@ const createDOMProps = (rnProps, resolveStyle = resolver) => {
       domProps.rel = `${domProps.rel || ''} noopener noreferrer`;
     }
   }
-  if (style != null) {
+  if (style) {
     domProps.style = style;
   }
-  if (typeof testID === 'string') {
+  if (testID && testID.constructor === String) {
     domProps['data-testid'] = testID;
   }
-  if (typeof type === 'string') {
+  if (type && type.constructor === String) {
     domProps.type = type;
   }