- PureComponent does a shallow object comparison on the props, and since you are passing in the same object reference, shouldComponentUpdate will return false and the updated data will not be rendered.This means that if any part of your app mutates data that needs to be rendered, PureComponent puts you at risk of displaying stale data.
- This is by far the biggest blocker because it results in incorrect UI behavior, and it is outside the control of your component.Fix: Never mutate values used as React props or state.
- Even if some ancestor component triggers a re-render, PureParent will not re-render because neither its state or props has changed.This gotcha also leads to incorrect UI behavior, but the issue is scoped to the component itself, making it easy to fix.Fix: Extract data dependency into state or props, and update state or props when the data changes.Object copyingQ: What happens when Parent is re-rendered with an unchanged props.dataList?A: PureChild is re-rendered wastefully because filter returns a new object, which tricks PureChild into thinking that the prop has changed.This problem is triggered by calling any function that creates a new object or using an inline object literal in render.Fix: Cache your derived data calculations.
- A: PureChild is re-rendered wastefully because arrow functions and Function.prototype.bind return new function instances, which tricks PureChild into thinking that the onClick handler has changed.Fix: Don’t use arrow functions and bind in render.
- When those props change, PureChild will re-render wastefully.Fix: Unless you’re writing some sort of higher-order-component, don’t be lazy and be explicit about the props that you are passing.ConclusionTurns out our app is littered with every single one of these gotchas, and is especially dependent on mutation side-effects.
We migrated our web app to React almost 3 years ago, and since React performs extremely well out of the box, optimizing performance was not something we had to worry about. However, as our…
Continue reading “Optimizing React Rendering (Part 1) – Flexport Engineering”
- React ComponentsIn this short post, I would like to describe how to structure react components.The main idea is to have a structure that helps to build highly maintainable and scalable software and makes it easy for developers to navigate and find files.Each component has its own directory and inside it, we put all related files.
- It will be also relatively easy to move components around or to create a separate package since all important code will be already packed up.Example componentsWe have to start with components directory which contains “global” components, used in different parts of an application.Above we can see Search / component, which is used in TopNavbar / and somewhere else in the app, that’s why both components are at the same main level.TopNavbar/ directory contains following files and directories:index.js – it contains only single line which exports TopNavbar default.
- /TopNavbar’;TopNavbar.jsx – main component structure (layout).
- Private components contain own tests, other private components, and styled-components.
- Stories for react-storybook are only created for the main component not for private ones.ConclusionAt first, this structure may look complex and overcomplicated.
The main idea is to have a structure that helps to build highly maintainable and scalable software and makes it easy for developers to navigate and find files. Each component has its own directory…
Continue reading “Structuring React Components – Kacper Goliński – Medium”
- They differ greatly in their approach, with Cordova being embedded web view centric, and React Native being native centric.
- React Native is just one of a growing number of frameworks for building mobile apps that are truly native after undergoing the build process.
- This presentation provides a short introduction to both Cordova and React Native, and walks through the process of migrating an example app — a fitness activity tracker — from Cordova to React Native, highlighting strategies, tips, and gotchas along the way.
- The presentation and full source code for the example app are available at:
Continue reading “Migrating from Cordova to React Native”
- We can build cross platform apps such as Android and IOS.React Native comes with the idea to code once and deploy everywhere so you don’t need to work twice to have your app running in different platforms.With React Native we can have almost all React library concepts including components, state, life-cycles methods and so on.
- All of them is classified as hybrid frameworks and runs inside a WebView but a React Native app are not a hybrid app because it do not run in a WebView.
- For this reason React Native apps are faster than hybrid apps and offer a better user experience.What is the advantages?The first and maybe one of the best advantages is the cross platform development capability.
- In addition to reducing the number of people responsible for one application, it is really very easy to code and get fast results because we don’t need to recompile the code every time we make a change!The other great advantage is that React Native is open source, so we don’t need to pay to use the framework and we also can submit pull requests to the core repository.How can I be more productive using it?You may heard somewhere that a good practice for a programmer is to reuse code.
This article is for you who have heard about this technology, but do not feel totally safe or/and do not have much time to get to know it.
So let’s get start with some questions. It is a framework…
Continue reading “A brief overview about React Native – Cristiano de Araujo – Medium”
- The map operator is a common way of transforming values emitted over time.
- In the following example, it passes each value through a transformation function “colored to black & white“:
Like map, the scan operator applies a function to a stream of values: an accumulator function.
- On the other hand, zip combines vertically the events of multiple event streams.
- It takes the n-th color and n-th shape to produce the n-th coloredShape:
Similarly to zip, combineLatest merges the events of multiple event streams.
- But whenever any event stream emits a value, combineLatest computes a new coloredShape using the latest color and the latest shape:
A new animated series will start soon.
In this new series we focus on operators for Reactive Programming. They are essential to react to data in your application.
Continue reading “Reactive Programming Operators (update 02/16)”
- The short answer is that you should very rarely, if ever use context in your own React components.
- Context acts like a portal in your application in which components can make data available to other components further down the tree without being passed through explictly as props.
- If an interim component does this, a child component won’t update, even if a context value changes:
In the above example, if changes, will not render, because its parent returned from .
- Libraries like React Router use context to allow the components that they provide application developers to communicate.
- It exposes the object on the context, and other than that it simply renders the children that it’s given:
expects to find , and it registers itself when it’s rendered:
Finally, we can use the and components in our own app:
The beauty of context in this situation is that as library authors we can provide components that can work in any situation, regardless of where they are rendered.
There is a lot of confusion amongst React developers on what context is, and why it exists. It’s also a feature that’s been hidden in the React documentation in the past and, although it is now documented on the React site I thought a post on its usage and when to use it would be of use.
Continue reading “Context in ReactJS Applications”