Components, Instances, and Elements | Lecture 121 | React.JS 🔥

The Coding Classroom

29 Nov 202305:10

Summary

TLDRThe video script delves into the conceptual differences between React components, component instances, and React elements. It explains that components are JavaScript functions that return React elements, serving as blueprints or templates for the UI. Component instances are the actual manifestations of these components, each holding its own state, props, and lifecycle. React elements, on the other hand, are immutable JavaScript objects created from component instances, containing information to generate DOM elements. The script highlights the journey from writing a component to rendering it as HTML in the DOM, clarifying the distinction between these key React concepts.

Takeaways

🔍 Components in React are essentially blueprints or templates for a piece of the UI, described using JSX syntax.
🛠️ A React component is a regular JavaScript function that returns React elements, forming an element tree.
🔄 Multiple instances of a component can be created from a single blueprint, each instance representing the component's physical presence in the component tree.
📦 Each component instance holds its own state and props, and goes through its own lifecycle, akin to a living organism.
🔄 Despite technical differences, the terms 'component' and 'component instance' are often used interchangeably in practice.
🔧 When a component is used in code, React elements are generated, which are immutable JavaScript objects kept in memory.
🔗 React elements contain all necessary information for creating DOM elements for the current component instance.
🎨 Ultimately, React elements are converted into actual DOM elements, which are then rendered to the screen by the browser.
🌐 The DOM elements are the final, visual representation of a component instance in the browser, not the React elements themselves.
🚀 The process from writing a component to it being rendered as HTML elements in the DOM illustrates the lifecycle of components in React applications.

Q & A

What is the conceptual difference between React components, component instances, and React elements?
-React components are the functions we write to describe a piece of the user interface, which return React elements. A component instance is the actual physical manifestation of a component in our componentry, created each time we use the component in our code. React elements are the immutable JavaScript objects created by calling React.createElement, containing information necessary to create DOM elements for the current component instance.
How are component instances created?
-React creates a new component instance each time we use the component in our code. For example, if a component is included three times in an app component, React will call the component function three times, creating three instances.
What does a component instance contain?
-Each component instance holds its own state, props, and lifecycle. It's like a living organism that can be born, live for some time, and eventually die.
What is the role of React elements?
-React elements are the result of using a component in our code. They are immutable JavaScript objects that React keeps in memory, containing information necessary to create DOM elements for the current component instance.
How are DOM elements created from React elements?
-React elements are not directly rendered to the DOM. Instead, they are converted to actual DOM elements, which are then painted onto the screen by the browser.
Can we use the terms 'component' and 'component instance' interchangeably?
-In practice, we often use the terms 'component' and 'component instance' interchangeably, even though 'component instance' would be more technically accurate when referring to the actual manifestation of a component in our componentry.
What is the purpose of JSX?
-JSX is a syntax extension that allows us to write React elements using a syntax that looks like HTML. Behind the scenes, JSX gets converted to multiple React.createElement function calls, which create the React elements.
What is the journey from writing a component to rendering it on the DOM?
-The journey starts with writing a component function, which is used multiple times in our code as a blueprint. Each time it is used, React creates a component instance, which returns a React element. This React element is then converted to actual DOM elements and painted onto the screen by the browser.
Why is understanding the difference between components, instances, and elements important?
-Understanding this difference is important because it helps clarify what actually happens with our components as we use them in our React applications. It's also a common interview question, so it's worth learning about this topic.
Can React elements directly influence the DOM?
-No, React elements themselves have nothing to do with the DOM. They simply live inside the React app and are used to create DOM elements when they are rendered on the screen.

Outlines

00:00

🧠 The Conceptual Differences Between React Components, Instances, and Elements

This paragraph explains the key differences between React components, component instances, and React elements. Components are JavaScript functions that describe a piece of the user interface by returning an element tree, typically using JSX syntax. Component instances are created when a component is used in the code, each with its own state, props, and lifecycle. React elements are immutable JavaScript objects containing the information needed to create DOM elements for a particular component instance. React elements are eventually converted to actual DOM elements and rendered in the browser. The paragraph emphasizes the journey from writing a component to rendering its instances as HTML elements in the DOM.

Mindmap

Keywords

💡React Components

React components are the building blocks of React user interfaces. They are regular JavaScript functions that return React elements, which are descriptions of the UI. As stated in the script, 'components are what we write, in order to describe a piece of the user interface.' Components act as blueprints or templates for UI elements.

💡Component Instances

Component instances are the actual physical manifestations of components living in the component tree. The script explains, 'React does this each time that we use the component, somewhere in our code.' For example, if a component is used three times, three instances of that component are placed in the component tree. Each instance holds its own state, props, and lifecycle.

💡React Elements

React elements are the result of using a component in our code. As mentioned in the script, 'a React element is basically the result of using a component in our code.' React elements are immutable JavaScript objects that contain all the information necessary to create DOM elements for the current component instance. They are not rendered directly to the DOM but are converted to DOM elements in the final step.

💡JSX

JSX is a syntax extension for JavaScript that allows developers to write HTML-like code in their JavaScript files. As stated in the script, 'we usually write these elements using the JSX syntax.' JSX is converted to React.createElement function calls behind the scenes, which create React elements.

💡State

State is an object that represents the internal data of a component. The script mentions that 'each instance, that holds its own state and props, and that also has its own life cycle.' State can change over time, and when it does, React re-renders the component and its children with the updated state.

💡Props

Props are short for properties, which are input data passed from a parent component to a child component. The script states that 'each instance, that holds its own state and props, and that also has its own life cycle.' Props are immutable and are used to customize the behavior and appearance of a component.

💡Component Lifecycle

The component lifecycle refers to the series of methods that are automatically called by React at specific points in a component's existence. As mentioned in the script, 'each instance, that holds its own state and props, and that also has its own life cycle.' These methods allow developers to perform actions at different stages of a component's lifecycle, such as when it is created, updated, or unmounted.

💡DOM Elements

DOM elements are the actual visual representations of components in the browser. The script states, 'the DOM elements are the actual, final, and visual representation, of the components instance in the browser.' React elements are converted to DOM elements, which are then painted onto the screen by the browser.

💡Blueprint

The script uses the term 'blueprint' to describe the nature of a component. It states, 'we can essentially think of a component as a blueprint, or a template, and it's out of this one blueprint, or template that React then creates one, or multiple component instances.' A blueprint is a design or plan that serves as a guide for creating something, in this case, component instances.

💡Immutable

Immutable means something that cannot be changed or modified after it is created. The script mentions that 'a React element is basically the result, of using a component in our code. It's simply a big immutable JavaScript object, that React keeps in memory.' React elements are immutable, meaning their properties cannot be altered directly after they are created.

Highlights

Components are what we write to describe a piece of the user interface, and they are regular JavaScript functions that return React elements.

A component is a generic description of the UI, like a blueprint or template, while React creates one or multiple component instances from this blueprint.

Each component instance holds its own state, props, and lifecycle, and can be born, live for some time, and eventually die, like a living organism.

In practice, we often use the terms 'component' and 'component instance' interchangeably, even though 'component instance' is technically more accurate.

As React executes the code in each component instance, it returns one or more React elements.

A React element is basically the result of using a component in our code, and it's an immutable JavaScript object that React keeps in memory.

A React element contains all the information necessary to create DOM elements for the current component instance.

The React element is eventually converted to actual DOM elements and painted onto the screen by the browser.

The DOM elements are the final, visual representation of the component instance in the browser.

React elements live inside the React app and have nothing to do with the DOM directly. They are simply converted to DOM elements when rendered.

The journey starts from writing a single component, using it multiple times as a blueprint, converting it to a React element, and finally rendering it as HTML elements into the DOM.

The conceptual difference between React components, component instances, and React elements is explained.

Understanding this difference will help make it clearer what actually happens with components as they are used.

This topic is a common interview question and worth learning about.

The process of creating React elements using JSX behind the scenes is mentioned.