Lifecycle Methods in React 16

This article is for developers with basic working knowledge of React. You will be introduced to the React components lifecycle methods, where they are called, how they are used and the thought process behind their implementation.

This is an overview of all the lifecycle methods in React 16, what they are used for and how they can be used in your workflow.

Introduction

React is a JavaScript library by Facebook with over 110,000 stars on GitHub. It is a declarative, efficient, and flexible framework for building user interfaces. It is really very painless to create interactive user interfaces, to build component-centric applications, which are both responsive and backward compatible. It is also currently arguably the most popular JavaScript framework out there according to the state of JS survey.

This article is for developers with basic working knowledge of React. You will be introduced to the React components lifecycle methods, where they are called, how they are used and the thought process behind their implementation.

React component lifecycle methods

React components lifecycle methods can be described as events that take place from any component’s inception to the death of that same component. The lifecycle of a React component takes place within these events that are in four categories:

1. Mounting: The methods and events that take place here happen as the component is mounted in the DOM.
2. Updating: Here the methods and events take place after the React component has entered the DOM.
3. Un-mounting: Here the methods and events take place as they React component leaves the DOM or is unmounted from the DOM.
4. Error Boundaries: Here is a special category that deals with handling or gracefully catching errors in order not to totally break your React application render.

In this post, the React lifecycle methods will be explained in the order they are called by React in the DOM.

constructor()

For React class components that are not functional components, the constructor is the very first method that gets called to action in the application’s component presentation. The constructor takes in props as an object, and you have to call the parent class through super in order to set access this.props to props ``inside the class. The constructor looks like this:

    class FirstComponent extends Component {
      constructor(props) {
        console.log("constructor is called here!");
        super(props);
        this.state = {
          counter: 0
        };
      }
    }

The super call is very important and it must have the props passed into it. It is also important to know that state can only be set inside constructors. You can also set state values, bind methods and even create refs inside the constructor.

getDerivedStateFromProps()

The very next method called after the constructor is the getDerivedStateFromProps method, it is a static method and so you cannot use this inside of it. It is also the last method called before the render method. It kind of has a specific use case, which is to return a state object on the initial props and set state, this can also be done with the constructor but the constructor does a lot more things aside from setting state. It is not a very frequently used method as many React developers just use the constructor instead. It takes two parameters, props and state and the syntax looks like this:

    static getDerivedStateFromProps(props, state) {
        console.log("getDerivedStateFromProps called here");
        return null;
      }

It is called on every render and it can be placed inside the constructor method.

render()

This is the most important method of any React class, the whole work that is going to appear in the DOM is done here as it outputs the JSX of your component. It is the most used React lifecycle method and it is the only required method in any React class.

    render(){
     console.log("render method is called here");
     return Hello world!

    }

You are not however allowed to set state inside the render method as it should be pure. Pure functions are functions without side effects, they must always return the same outputs when the same corresponding inputs are passed into them.

componentDidMount()

This method is called immediately after the render method call as soon as the component is mounted. Inside this method is where you are allowed to do all the behind the scenes work you need without the DOM. These things can range from setting state, initializing and loading data and even adding event listeners. The syntax looks like this:

    componentDidMount() {
     console.log("componentDidMount was called here");
    }

If setState is called inside this method, the DOM is re-rendered to reflect the modification. This method is perfect for making AJAX calls.

shouldComponentUpdate()

This is the method that is called right after the componentDidMount method, this method does not allow you set state in it. It is useful for when you do not want your props or state changes re-rendered, it is like a bridge where you have to get permission if a component should be updated based on the props or state changes made. It returns a boolean, usually true by default. The syntax looks like this:

    shouldComponentUpdate(nextProps, nextState) {
      console.log("should component update is called here!");
      return nextState.cars.length < this.state.cars.length;
    }

It takes in two arguments, nextProps and nextState and with those you can you can make your return conditions for the re-render. It is advised that this method be used with care and for optimization purposes keep in mind that it can trigger re-renders.

getSnapshotBeforeUpdate()

This method is a very frequently used method, it is called just between the period a component is rendered and when it is updated in the DOM. It is a kind of screenshot of what the previous state and props looks like before updating, a genius method by React. The syntax can look like this:

    getSnapshotBeforeUpdate(prevProps, prevState){
      console.log("getSnapshotBeforeUpdate was called here!");
      if (prevState.cars.length < this.state.cars.length) {
        return { lastVehicle };
      }
      return null;
    }

It takes two parameters, prevProps and prevState and it either returns a value from the conditional statement or null by default. The value returned is always passed down to the componentDidUpdate method.

componentDidUpdate()

This is the next method that gets called immediately after the getSnapshotBeforeUpdate method, right after a DOM update. Here some logic can be set up for actions on an updated DOM. The syntax is like this:

    componentDidUpdate(prevProps, prevState, snapshot) {
      console.log("componentDidUpdate was called here!");
    if (snapshot.lastVehicle) {
        return  No cars left! 

      }
    }

It has three parameters, the prevProps, prevState and the snapshot . The snapshot is the value returned from the getSnapshotBeforeUpdate method. You can set state here but it should always be inside a conditional statement.

componentWillUnmount()

This method is called just before a component is unmounted from the DOM, it is the method called right after componentDidUpdate. Here is where your clean up logic should go, clearing counters and caches, cancel API requests or removing things like event listeners. It can look like this:

    componentWillUnmount(){
      console.log("componentWillUnmount was called here!");
      window.removeEventListener("restart");
    }

As you might have guessed, you cannot set state in this method because that would automatically have to cause a re-render most times. After this, your component is gone, for good.

getDerivedStateFromError()

This is one of the two new lifecycle method used to gracefully handle errors called error boundaries. If a child component of a parent component has an error we can use this method to display an error screen. The syntax looks like this:

    static getDerivedStateFromError(error) {
        // Update state so the next render will show the fallback UI.
        return { hasError: true };
      }

      render() {
        if (this.state.hasError) {
          // You can render any custom fallback UI
          return # Something went wrong.
;
        }

        return this.props.children; 
      }

Here we catch a child component error and we display an error message of choice to the client gracefully instead of breaking the application or displaying a blank screen.

componentDidCatch()

This is the second lifecycle method that is a React error boundary. It enhances the capability of the first error boundary above by allowing for logging errors. The syntax looks like this:

    componentDidCatch(error, info) {
        console.log(info.componentStack);
      }

So, in addition to showing your client a decent ‘something went wrong’ message in the user interface, you also get a platform to inform a developer inspecting the component of specific information about the error. It is mostly used in addition with the getDerivedStateFromError method.

Conclusion

You have seen all the lifecycle methods in React 16, their syntax and how they all work in the chronological order of method calls. The error boundaries are relatively new and you should make sue to incorporate them in your workflow, they have been found to be very helpful. You can see a visual representation of these methods here.

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How native is React Native? | React Native vs Native App Development

If you are undertaking a mobile app development for your start-up or enterprise, you are likely wondering whether to use React Native. As a popular development framework, React Native helps you to develop near-native mobile apps. However, you are probably also wondering how close you can get to a native app by using React Native. How native is React Native?

In the article, we discuss the similarities between native mobile development and development using React Native. We also touch upon where they differ and how to bridge the gaps. Read on.

A brief introduction to React Native

Let’s briefly set the context first. We will briefly touch upon what React Native is and how it differs from earlier hybrid frameworks.

React Native is a popular JavaScript framework that Facebook has created. You can use this open-source framework to code natively rendering Android and iOS mobile apps. You can use it to develop web apps too.

Facebook has developed React Native based on React, its JavaScript library. The first release of React Native came in March 2015. At the time of writing this article, the latest stable release of React Native is 0.62.0, and it was released in March 2020.

Although relatively new, React Native has acquired a high degree of popularity. The “Stack Overflow Developer Survey 2019” report identifies it as the 8th most loved framework. Facebook, Walmart, and Bloomberg are some of the top companies that use React Native.

The popularity of React Native comes from its advantages. Some of its advantages are as follows:

• Performance: It delivers optimal performance.
• Cross-platform development: You can develop both Android and iOS apps with it. The reuse of code expedites development and reduces costs.
• UI design: React Native enables you to design simple and responsive UI for your mobile app.
• 3rd party plugins: This framework supports 3rd party plugins.
• Developer community: A vibrant community of developers support React Native.

Why React Native is fundamentally different from earlier hybrid frameworks

Are you wondering whether React Native is just another of those hybrid frameworks like Ionic or Cordova? It’s not! React Native is fundamentally different from these earlier hybrid frameworks.

React Native is very close to native. Consider the following aspects as described on the React Native website:

• Access to many native platforms features: The primitives of React Native render to native platform UI. This means that your React Native app will use many native platform APIs as native apps would do.
• Near-native user experience: React Native provides several native components, and these are platform agnostic.
• The ease of accessing native APIs: React Native uses a declarative UI paradigm. This enables React Native to interact easily with native platform APIs since React Native wraps existing native code.

Due to these factors, React Native offers many more advantages compared to those earlier hybrid frameworks. We now review them.

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 Component Life Cycle in React

Every component in React goes through a lifecycle of events. You can think is of going through a cycle of birth, growth, and death the same as the picture below.

The phases are:

• Initialization — Starting the journey of your component
• Mounting — Birth of your component
• Update — Growth of your component
• Unmount — Death of your component

1. Initialization

This is the phase in which the component is going to start its journey. The developer has to define the props and initial state of the component. This is usually done inside the constructor method (see below to understand the initialization phase better).

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How to Select and Hire the Best React JS and React Native Developers?

Since March 2020 reached 556 million monthly downloads have increased, It shows that React JS has been steadily growing. React.js also provides a desirable amount of pliancy and efficiency for developing innovative solutions with interactive user interfaces. It’s no surprise that an increasing number of businesses are adopting this technology. How do you select and recruit React.js developers who will propel your project forward? How much does a React developer make? We’ll bring you here all the details you need.

What is React.js?

Facebook built and maintains React.js, an open-source JavaScript library for designing development tools. React.js is used to create single-page applications (SPAs) that can be used in conjunction with React Native to develop native cross-platform apps.

React vs React Native

• React Native is a platform that uses a collection of mobile-specific components provided by the React kit, while React.js is a JavaScript-based library.
• React.js and React Native have similar syntax and workflows, but their implementation is quite different.
• React Native is designed to create native mobile apps that are distinct from those created in Objective-C or Java. React, on the other hand, can be used to develop web apps, hybrid and mobile & desktop applications.
• React Native, in essence, takes the same conceptual UI cornerstones as standard iOS and Android apps and assembles them using React.js syntax to create a rich mobile experience.

What is the Average React Developer Salary?

In the United States, the average React developer salary is $94,205 a year, or $30-$48 per hour, This is one of the highest among JavaScript developers. The starting salary for junior React.js developers is $60,510 per year, rising to $112,480 for senior roles.

* React.js Developer Salary by Country

• United States- $120,000
• Canada - $110,000
• United Kingdom - $71,820
• The Netherlands $49,095
• Spain - $35,423.00
• France - $44,284
• Ukraine - $28,990
• India - $9,843
• Sweden - $55,173
• Singapore - $43,801

In context of software developer wage rates, the United States continues to lead. In high-tech cities like San Francisco and New York, average React developer salaries will hit $98K and $114per year, overall.

However, the need for React.js and React Native developer is outpacing local labour markets. As a result, many businesses have difficulty locating and recruiting them locally.

It’s no surprise that for US and European companies looking for professional and budget engineers, offshore regions like India are becoming especially interesting. This area has a large number of app development companies, a good rate with quality, and a good pool of React.js front-end developers.

As per Linkedin, the country’s IT industry employs over a million React specialists. Furthermore, for the same or less money than hiring a React.js programmer locally, you may recruit someone with much expertise and a broader technical stack.

How to Hire React.js Developers?

• Conduct thorough candidate research, including portfolios and areas of expertise.
• Before you sit down with your interviewing panel, do some homework.
• Examine the final outcome and hire the ideal candidate.

Why is React.js Popular?

React is a very strong framework. React.js makes use of a powerful synchronization method known as Virtual DOM, which compares the current page architecture to the expected page architecture and updates the appropriate components as long as the user input.

React is scalable. it utilises a single language, For server-client side, and mobile platform.

React is steady.React.js is completely adaptable, which means it seldom, if ever, updates the user interface. This enables legacy projects to be updated to the most new edition of React.js without having to change the codebase or make a few small changes.

React is adaptable. It can be conveniently paired with various state administrators (e.g., Redux, Flux, Alt or Reflux) and can be used to implement a number of architectural patterns.

Is there a market for React.js programmers?
The need for React.js developers is rising at an unparalleled rate. React.js is currently used by over one million websites around the world. React is used by Fortune 400+ businesses and popular companies such as Facebook, Twitter, Glassdoor and Cloudflare.

Final thoughts:

As you’ve seen, locating and Hire React js Developer and Hire React Native developer is a difficult challenge. You will have less challenges selecting the correct fit for your projects if you identify growing offshore locations (e.g. India) and take into consideration the details above.

If you want to make this process easier, You can visit our website for more, or else to write a email, we’ll help you to finding top rated React.js and React Native developers easier and with strives to create this operation

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React 17 Example Tutorials

React 17 tutorials. Here, you can find basic to advance react 17 tutorial.

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Using React Hooks instead of lifecycle methods

How to replace React lifecycle methods with React Hooks in functional components? First, let’s see to lifecycle methods diagram.

You don’t need the constructor method in functional components. Use the [useState](https://reactjs.org/docs/hooks-state.html)Hook to initialize the state.

The common React component lifecycle methods arecomponentDidMount,``componentDidUpdate and componentWillUnmount. For all cases we should use the [useEffect](https://reactjs.org/docs/hooks-effect.html)Hook. Let’s see an example for details.

//componentDidMount and componentDidUpdate. An effect re-runs every render

	useEffect(() => {
	    // to do smth...
	})

	//componentDidMount. An effect runs only on mount

	useEffect(() => {
	    // to do smth...
	}, [])
view raw
demo.tsx hosted with ❤ by GitHub

For componentWillUnmount method, we should add the return statement to the useEffect Hook.

useEffect(() => {
	  // to do smth...

	  return () => {
	    // to do smth else when a component is unmounted...
	  }
	})
view raw
demo.tsx hosted with ❤ by GitHub

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