React.js - Everything You Need To Know
# What is React.js
# How React.js Works
React.js works by breaking down user interfaces into small, reusable components. Each component is responsible for rendering a specific part of the UI and can receive data from its parent component in the form of props. When the data or state of a component changes, React will update the component’s UI accordingly.
React uses a virtual DOM, which is a lightweight in-memory representation of the actual DOM, to optimize updates and minimize the number of actual DOM manipulations required. When a component’s state or props change, React will update the virtual DOM, determine the minimum number of changes required to update the real DOM, and then make those updates.
React also uses a one-way (unidirectional) data flow, meaning that data is passed down from parent components to child components through props, but cannot be changed directly by the child components. Instead, child components can trigger changes in their parent components by calling event handlers.
By breaking down user interfaces into components, React allows developers to build complex, dynamic UIs in a modular and maintainable way. This makes it easier to understand, test, and scale your application over time.
# What are components in React
Components in React are the building blocks of a React application. They are reusable pieces of UI that represent a specific aspect of the user interface. There are two types of components in React - functional components and class components.
# What is a functional component in React
Functional components have no state or lifecycle methods, and can only receive props as input. They are often used for presentational components that only need to render UI based on the props they receive, and do not need to keep track of any internal state.
# What is a class component in React
React.Component base class. Class components are used to define components that need to keep track of their own internal state, or have lifecycle methods.
Class components have access to the
state property, which can be used to store component-specific data, and lifecycle methods, which are hooks into the component’s lifecycle that can be used to perform certain actions at specific points in the component’s lifecycle, such as when the component is mounted or updated.
# How to create a component in React
You can create a component in React using either a function or a class.
Here’s an example of a functional component.
And here’s an example of a functional component that does the same thing.
# What is JSX in React
# How to use props in React
# What is state in React and when to use it
State is an object that holds the data that a component needs to render. It’s used to store data that changes dynamically within a component. You should use state when you need to update the UI based on user interactions or other events.
# What is the difference between props and state in React
Props are data that are passed from a parent component to a child component. They are read-only and cannot be changed by the child component. State, on the other hand, is data that is managed within a component and can change based on user interactions or other events.
# How to handle events in React
Events in React can be handled using the
on syntax. For example, to handle a button click event, you can use
# How to render multiple components in React
You can render multiple components by returning an array of components from the render method, or by wrapping multiple components in a parent component.
In this example I’m wrapping the components
Goodbye in a single
# What is the Virtual DOM in React and why use it
The Virtual DOM is a virtual representation of the actual DOM in a React application. It’s used to update the actual DOM efficiently by only making the minimum necessary changes. This leads to improved performance, especially in applications with a large number of dynamic updates.
# How to pass data from a child component to a parent component in React
To pass data from a child component to a parent component, you can pass a callback function as a prop from the parent component to the child component. The child component can then call the callback function when it needs to pass data to the parent component.
# What are the lifecycle methods in React
The lifecycle method in React are methods that are automatically called at specific points in the lifecycle of a component. They allow you to perform certain actions when a component is created, updated, or destroyed. Some common lifecycle methods are
# How to use conditional rendering in React
Conditional rendering in React allows you to conditionally render components based on certain conditions. There are several ways to do conditional rendering in React, using the ternary operator,
if statements, and
Here’s an example of conditional rendering in React using a ternary operator.
In this example, the
User component takes a
user prop and uses a ternary operator to conditionally render either a div containing the user’s name and email or a message indicating that no user was found.
The same conditional rendering functionality can be achieved using an
# How to use styles in React
There are several ways to add styles in React, including using inline styles, CSS classes, and CSS modules.
Here’s an example of using inline styles.
In this example, the
Box component takes a
color prop and uses an object literal to define inline styles for the component. The styles are then passed as the value of the
style prop to a
# What are React hooks
React Hooks are a feature in React that allow you to add state and other React features to functional components. Prior to Hooks, adding state and other React features to functional components required converting them to class components, which can be verbose and often lead to unnecessary code.
Hooks let you reuse stateful logic, without writing a class component.
# What are the standard React hooks
There are ten standard React hooks that are part of the React core library and are available for use in your projects out of the box. They provide a way to add functionality and state management to functional components without writing a class component.
useState: adds state to functional components
useEffect: adds side effects to functional components
useContext: allows functional components to access context
useReducer: adds reducer-based state management to functional components
useCallback: memoizes a function component
useMemo: memoizes a value component
useRef: creates a reference to a DOM element or a value
useImperativeHandle: customizes the behavior of components exposed to parent components
useLayoutEffect: runs effects synchronously immediately after a render
useDebugValue: displays a custom label for a hook in React DevTools
# What is a
useState hook in React and how to use it
useState Hook in React allows you to add state to functional components. It takes an initial state value as an argument and returns an array with two elements: the current state value and a function to update it.
Here’s an example using the
useState Hook to add state to a functional component
In this example, the
useState Hook is used to manage the state of a counter in the
useState Hook returns an array with two elements, the current state value (
count) and a function to update it (
count value is displayed in a paragraph element, and a button is provided that will increment the count when clicked.
# What is a
useEffect hook in React and how to use it
useEffect Hook in React allows you to run some side effects in your functional components, such as API calls, updating the DOM, or subscriptions. It takes two arguments: a callback function that contains the side effects and a dependency array that tells React when to re-run the effect.
Here’s an example of how to use the
useEffect Hook in a functional component.
In this example, the
useEffect Hook is used to update the document title whenever the count state changes.
useEffect Hook takes a callback function as its first argument, which updates the document title to reflect the current count. The second argument is a dependency array that tells React to re-run the effect whenever the count state changes.
It’s important to note that effects run on every render by default, including the first render.
If you want an effect to run only once, pass an empty dependency array
 as the second argument to the
useEffect Hook. This will tell React to run the effect only on the first render and never re-run it.
# What is a
useContext hook in React and how to use it
useContext Hook in React allows you to access data from a context object in your functional components. Context provides a way to pass data through the component tree without having to pass props down manually at every level.
Here’s an example of how to use the
useContext Hook in a functional component.
Here’s what happens in this example:
- Create a context object using the
createContextfunction, which takes an initial value as an argument.
- Use the
useContextHook in the
Childcomponent to access the value from the context object.
- Wrap the
Childcomponent in a
MyContext.Providercomponent and pass a value prop to it. This makes the value from the context object available to all children components that use the
The value from a context object can only be accessed from functional components that are descendants of a context provider, which means that the context provider must be a parent or ancestor of the functional component that uses the
# Is React.js worth learning
Yes. React is worth learning if you’re interested in becoming a front-end engineer. React is known for its simplicity, flexibility, and performance, making it an excellent choice for building complex and dynamic web applications. It has a large community of developers who contribute to its development and provide support, making it easy to find help and resources when needed.
# How Much React.js Developers Make
The salary of a React.js developer can vary depending on factors such as location, experience, and job title. As a beginner you shouldn’t expect a salary above $100k/year.
Here are some salaries for different proficiency level of a React.js dev in the US:
- Junior React.js developer: $70,000 - $110,000
- Mid-level React.js developer: $110,000 - $140,000
- Senior React.js developer: $140,000 - $180,000
- React.js architect: $150,000 - $200,000
# How Long Will It Take To Learn React.js
It depends on your current level and the amount of time you dedicate towards learning. If you’re already familiar with the basics of web development using HTML, CSS and JS, then you can learn React as fast as 100 hours or 1 month of deliberate practice.
If you’re starting from scratch, then you should can safely add 200 hours or 2 months of intense practice to learn HTML, CSS and JS.
Note: Watching YouTube videos on autopilot isn’t practice, it’s procrastination.
# Why we use React Instead of HTML
React is not a replacement for HTML. While HTML provides the basic structure of a web page, React provides the dynamic and interactive features of it.
Here are core benefits of choosing React over plain HTML.
- Reusability: React components can be reused across multiple pages or even different applications, making your code more modular and efficient.
- Virtual DOM: React uses a virtual DOM to update the user interface efficiently and with minimal reloads, improving the overall user experience.
- Data Binding: React uses a unidirectional data flow, which makes it easier to manage and update the state of your application.
- Interactivity: React makes it easy to add interactivity to your application, such as event handling and dynamic updates.
- Dynamic Content: React allows you to dynamically render content based on user interactions or changes to your application data.
# Why is React So Popular
Here’s a list of reasons why React is so popular in the web development world.
- Ease of Use: React’s simple and intuitive API makes it easy to learn and use, even for beginners.
- Performance: React’s use of a virtual DOM, combined with its efficient updates, results in fast and responsive user interfaces.
- Community: React has a large and active community of developers, which means that there is a wealth of resources, tutorials, and libraries available to help you get started and solve problems.
- Ecosystem: React can be used with a variety of other technologies, such as Redux for state management, GraphQL for data management, and React Native for building mobile apps, making it a versatile and flexible choice.
- Job Demand: React is used by many companies and organizations, from startups to large enterprises, and the demand for React developers continues to grow, making it a valuable skill to have for your career.