Understanding React : Components, Instances, and Element

In this post, we'll explore the nuanced differences between React components, component instances, and React elements - concepts that are crucial for a deeper understanding of React's inner workings.

React Components

At its core, a React component is a function (or class) that returns React elements. Think of it as a blueprint for a piece of your user interface. It's a reusable, modular unit that encapsulates structure, behavior, and style.

Simply, a component is just a simple function that describes a piece of our website. It's like a recipe for a part of your user interface.

Consider, we are creating a MagicButton component:

function MagicButton({ label, onClick }) {
  return (
    <button className="btn" onClick={onClick}>
      {label}
    </button>
  );
}

This MagicButton is our blueprint. It's not a real button yet – it's just the idea of a button, waiting to be brought to life.

Component Instances

When we use a component in your JSX, like <MagicButton label="Submit" onClick={handleSubmit} />, React creates a component 'instance' of that component. Each instance is a unique entity with its own props and state (if any).

Let's look at a following example:

function App() {
  return (
    <div>
      <MagicButton label="Open Sesame" onClick={handleCaveEntrance} />
      <MagicButton label="Cast Spell" onClick={handleSpellCasting('healing')} />
      <MagicButton label="Summon Dragon" onClick={summonCreature('dragon')} />
    </div>
  );
}

In this App component, we're creating three instances of the Button component. Each instance is independent, with its own set of props and its own lifecycle.

React Elements

As React processes your components, it generates React elements. These elements are plain JavaScript objects that describe what you want to see on the screen. They're lightweight, stateless, and immutable.

These elements are just JavaScript objects that describe what should appear on the screen. React uses these instructions to figure out how to create the actual parts of your website that people can see and click on.

When you write JSX like <MagicButton label="Open Sesame" />, it gets transpiled to:

React.createElement(MagicButton, { label: "Open Sesame" });

This createElement call returns a React element, which might look something like this:

{
  type: Button,
  props: { label: "Open Sesame" },
  key: null,
  ref: null,
}

This object is React's intermediate representation of your component instance. It's not a DOM element, but rather a description of what DOM element should be created.

From Elements to the Screen

React takes these elements and uses them to efficiently update the DOM. It compares new elements with the previous render, determining the minimal set of changes needed to bring the DOM in line with the new desired state.

This process, known as reconciliation, is what gives React its performance edge. By working with this lightweight representation (React elements) instead of directly manipulating the DOM, React can batch and optimize updates for maximum efficiency.

The Lifecycle of a Component

Understanding this journey helps clarify the component lifecycle:

1. You define a component (the blueprint).

2. React creates instances of this component as needed.

3. These instances generate React elements during the render process.

4. React uses these elements to update the actual DOM.

This cycle repeats every time there's a state change or new props are passed down, with React efficiently determining what actually needs to change in the DOM.

We hope you found this explanation insightful. Keep an eye out for our future articles where we'll delve deeper into advanced React concepts and best practices. Until then, happy coding! 🚀