Props vs State – ReactJS

ReactJS, a popular JavaScript library for creating user interfaces, has completely transformed front-end development. It drills down on building reusable ‘components’, each managing their own state and props. The terms ‘State’ and ‘Props’ are fundamental concepts every React developer needs to understand. However, they can be easily misunderstood regardless of the developer’s level of expertise.

State and Props enable components to interact with each other by passing data or functionality. However, their usage and functionality differ in several aspects. Let’s delve into each concept and examine the differences between the two.

React State

State is essentially a data structure that a React component can hold and change over its lifespan. It is mutable and locally scoped. This implies that each component’s state is managed inside that component and can be changed internally by the component itself. Think of a state as a local storage that only that specific component has sole control of and can manipulate at will.

State is used for data that will change over time. For instance, user input, or data fetched from an API that will change each time they make a request, like a live score in a sports match.

In a class component, the state object is initialized in the constructor, and then it can be altered with the setState() function. In functional components, the useState() hook is used to manage the state.

React Props

Props, short for “Properties,” are equivalent to parameters passed into a function. The primary purpose of props in React is to provide component functionality or data from a parent component to a child component. Unlike State, props are read-only. This means they cannot be changed by the components receiving them, making them immutable. Props ensure that components become more dynamic and reusable.

You might start to see how different these concepts are when you start passing State data from a parent component to its child component via Props.

For instance, let’s say you have a parent component with a state variable ‘color’. You can pass this ‘color’ to a child component like so

<ChildComponent color={this.state.color}/>

Here, ‘color’ is a prop for ChildComponent, and it can use this prop as per its needs. However, if ChildComponent tries to modify the prop, it will result in an error because, as already mentioned, props are read-only.

The Key Differences

The key differences between State and Props can be summed up as follows:

  1. Mutability: State is mutable and can be changed within a component. Props, conversely, are immutable and cannot be changed once passed from a parent component to a child component.
  2. Scope: State is scoped to the component in which it is declared, while Props data is passed from a parent component to a child component.
  3. Life span: The life span of State lasts as long as the component is mounted on the DOM, whereas props cease to exist once the component is unmounted.
  4. Role: State is used when a component’s data will change over time, whereas Props are used to pass data or functionality from parent components to child components.

In conclusion, while state and props in ReactJS might seem similar, they serve fundamentally different purposes. The state provides components with mutable, component-scoped, and persisting data. Props, on the other hand, pass read-only attributes from one component hierarchy to a child component. A clear comprehension of these differences is fundamental to working proficiently with ReactJS.

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