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React recently introduced an experimental profiler API. This page gives instructions on how to use this API in a production release of your app.

Table of Contents

Profiling in production
- Create React App
- Webpack 4
Troubleshooting
- Tracing broke after an NPM update

Profiling in production

Profiler

React 16.4 will introduce a new Profiler component (initially exported as React.unstable_Profiler) for collecting render timing information in order to measure the "cost" of rendering for both sync and async modes.

Profiler timing metrics are significantly faster than those built around the User Timing API, and as such we plan to provide a production+profiling bundle in the future. (The initial release will only log timing information in DEV mode, although the component will still render its children- without timings- in production mode.)

How is it used?

Profiler can be declared anywhere within a React tree to measure the cost of rendering that portion of the tree. For example, a Navigation component and its descendants:

	import React, { Component } from 'react';
	import firebase from '@firebase/app';
	import firestore from './firestore'; // Code: https://gist.github.com/sconstantinides/546a48ba183b1234f750ca6261440199

	class App extends Component {
	constructor(props) {
	super(props);

	this.state = {
	userId: localStorage.getItem('userId') \|\| '',

	const path = require('path')

	const sharedBlacklist = []

	const platformBlacklists = {
	ios: [
	'.web.js',
	'.macos.js',
	/node_modules\/react-native-web\/.*/,
	/node_modules\/react-native-windows\/.*/,

	# this should be the folder name under `ios` for your project
	project_name = 'MyProject'

	# NOTE: This is meant to be run on CI where it changes everything before building the app.
	# Usage:
	# `RN_RELEASE_TYPE=beta fastlane prep_release_type` (on CI these ENV variables should be set via the UI)
	# Available release types: alpha, beta, production (default)
	#
	# If you're trying this script out locally, make sure you have ImageMagick installed, and discard the changes via git when you're done.
	desc "Updates the app identifier, display name and icon for alpha, beta, and production releases"

	/* eslint no-useless-escape: 0 */
	/* eslint max-len: 0 */
	/**
	* For more info regarding metro config:
	* @see https://facebook.github.io/metro/docs/en/configuration
	*/
	const path = require("path");
	const fs = require("fs");

	// Get blacklist factory

	// Demo: https://snack.expo.io/@brunolemos/touch-button-scale-effect

	import React from 'react'
	import { Animated, StyleProp, TouchableWithoutFeedback, TouchableWithoutFeedbackProps, ViewStyle } from 'react-native'
	import { styleMerge } from 'shared/src/utils'

	export interface TouchableScaleProps extends TouchableWithoutFeedbackProps {
	containerStyle?: StyleProp<ViewStyle>
	}

	import {
	Dimensions,
	LayoutChangeEvent,
	Platform,
	ScrollEvent,
	ScrollView,
	StyleSheet,
	View,
	} from "react-native";
	import {Font, Space} from "../atoms";

	import React from 'react';

	const ConditionalWrap = ({condition, wrap, children}) => condition ? wrap(children) : children;

	const Header = ({shouldLinkToHome}) => (
	<div>
	<ConditionalWrap
	condition={shouldLinkToHome}
	wrap={children => <a href="/">{children}</a>}
	>