React useState() hook introduction 🎣

Summary

In this video, the presenter introduces React Hooks, a feature that enables functional components to use React features without writing class components, introduced in React 16.8. The focus is on the useState hook, which allows for stateful variables and their update functions. The tutorial walks through creating a reactive counter program, demonstrating how to use useState to manage state changes that trigger re-renders in the virtual DOM. The video also covers creating stateful variables for name, age, and Boolean values, and concludes with styling the counter with CSS.

Takeaways

• 📌 React hooks were introduced in version 16.8, allowing functional components to use state and other React features without writing class components.
• 🔑 The `useState` hook is fundamental for creating stateful variables and their setter functions within functional components.
• 💡 Using `useState` provides a way to update state and trigger re-renders in the React virtual DOM, unlike regular variables which do not cause re-renders.
• 🛠️ The `useState` hook returns an array with two elements: the current state value and a function to update it.
• 📝 When using `useState`, you can optionally pass an initial state value; if not provided, it defaults to `null`.
• 🔄 The script demonstrates creating a counter program using `useState` to manage incrementing, decrementing, and resetting a count.
• 🎨 Conditional rendering is shown by toggling a Boolean state to display 'yes' or 'no' based on its value.
• 👩‍💻 The video includes a step-by-step guide on setting up a new React component and using hooks within it.
• 🌐 The script covers the necessity of importing React and destructuring `useState` from it to use within functional components.
• 🖌️ CSS styling is applied to enhance the visual presentation of the counter component, demonstrating the integration of React functionality with styling.

Q & A

What is a React Hook?

A React Hook is a special function that allows functional components to use React features without writing class components. It was introduced in React version 16.8.

Why were React Hooks introduced?

React Hooks were introduced to allow developers to use state and other React features in functional components without the need to write class components.

What is the most widely used React Hook?

The most widely used React Hook is `useState`, which allows the creation of a stateful variable and a setter function to update its value.

How does the `useState` hook work?

The `useState` hook returns an array with two elements: a stateful variable and a setter function. The setter function is used to update the state, which triggers a re-render of the component.

Can you provide an example of how to use the `useState` hook?

To use `useState`, you import it from React and call it within a functional component. For example, `const [name, setName] = useState('');` creates a stateful variable `name` and a setter function `setName`.

What is the purpose of the setter function returned by `useState`?

The setter function returned by `useState` is used to update the stateful variable. When called with a new value, it updates the state and causes the component to re-render with the new state.

How can you set an initial state with `useState`?

You can set an initial state by passing it as an argument to the `useState` hook. For example, `const [age, setAge] = useState(0);` sets the initial state of `age` to 0.

What is the difference between a normal variable and a stateful variable in React?

A normal variable does not trigger a re-render when updated, whereas a stateful variable created with `useState` does trigger a re-render, allowing the UI to reflect the updated state.

Can you explain the concept of conditional rendering in the context of the `useState` hook?

Conditional rendering with `useState` can be achieved using logical operators to determine what to display based on the state. For example, `isEmployed ? 'Yes' : 'No'` will display 'Yes' if `isEmployed` is true, and 'No' otherwise.

How do you create a counter program using React Hooks?

To create a counter program, you use the `useState` hook to manage the count state and provide functions to increment, decrement, and reset the count. These functions are then used as event handlers for buttons in the component's JSX.

What are some other React Hooks mentioned in the script?

Other React Hooks mentioned in the script include `useEffect`, `useContext`, `useReducer`, and `useCallback`, each serving different purposes such as managing side effects, providing context, and optimizing performance.

Outlines

00:00

🛠️ Introduction to React Hooks

The paragraph introduces the concept of React Hooks, explaining that they are special functions allowing functional components to utilize React features without writing class components. This was introduced in React version 16.8. The paragraph also discusses the 'useState' hook, which is the most commonly used. It allows for the creation of a stateful variable and a setter function to update its value. The video aims to create a reactive counter program using the useState hook by the end.

05:01

🎯 Creating a Stateful Variable with useState

This section provides a step-by-step guide on using the 'useState' hook to create a stateful variable and a setter function in a functional component. It explains the process of importing the hook, using array destructuring to extract the stateful variable and setter function, and updating the stateful variable with the setter function. The paragraph also includes a practical example where a 'name' variable is updated using a button click, demonstrating the re-rendering of the virtual DOM when the stateful variable is changed.

10:01

🔢 Incrementing and Toggling State with useState

The paragraph delves into creating additional stateful variables such as 'age' and a Boolean 'isEmployed'. It explains how to increment the 'age' variable by one or more with each button click and toggle the 'isEmployed' Boolean value between true and false. The video script includes the code for creating these variables, updating them, and rendering the updated values in the UI. It also touches on conditional rendering using the ternary operator for displaying the 'isEmployed' status.

15:04

🔄 Building a Counter Program with useState

The final paragraph focuses on building a counter program using the 'useState' hook. It outlines the creation of a 'count' stateful variable with initial value zero and functions to increment, decrement, and reset the counter. The paragraph includes the JSX code for rendering the counter, buttons for controlling the counter, and a brief mention of styling the counter component with CSS. The video script concludes with a demonstration of the counter functionality and a summary of the 'useState' hook's capabilities.

Keywords

💡React Hooks

React Hooks are functions that allow you to 'hook into' React state and lifecycle features from functional components. In the video, the presenter explains that hooks were introduced in React version 16.8, enabling developers to use React features without writing class components. Hooks like `useState` and `useEffect` are mentioned as examples, which are used to manage state and side effects in function-based components respectively.

💡useState

The `useState` hook is a fundamental React Hook that lets you add state to functional components. The video script describes `useState` as a way to create a stateful variable and a setter function to update its value. This hook is crucial for building interactive UIs, as it allows for the dynamic updating of the component's state, which in turn updates the virtual DOM.

💡Functional Components

Functional components in React are functions that return a React element. The video emphasizes the shift from class components to functional components facilitated by hooks. Before hooks, stateful logic was typically managed in class components, but now functional components can handle state and lifecycle through hooks, making them more concise and easier to manage.

💡Class Components

Class components are a type of component in React that use ES6 class syntax. The video script contrasts class components with functional components, noting that prior to hooks, state management and lifecycle features were only available in class components. Hooks have since made it unnecessary to write class components for stateful logic in many cases.

💡Virtual DOM

The Virtual DOM (Document Object Model) is a programming concept where an in-memory representation of the DOM is kept and updated, minimizing actual DOM manipulations for performance. The script explains that when the state is updated using the `useState` hook, the change is reflected in the virtual DOM, which then triggers a re-render of the component.

💡Array Destructuring

Array destructuring is a JavaScript feature that allows for the extraction of values from arrays. In the context of the video, array destructuring is used to extract the state variable and its updater function from the array returned by the `useState` hook. This makes it easier to work with the state and its updater function as separate variables.

💡Stateful Variable

A stateful variable is a variable that holds a value that can change over time. The video script uses the term to describe the variable created by the `useState` hook. Unlike normal variables, stateful variables in React are part of the component's state, and their updates can trigger re-renders of the component.

💡Setter Function

A setter function is a function that sets or updates the value of a variable. In the video, the presenter explains that the `useState` hook returns an array containing a stateful variable and its corresponding setter function. This setter function is used to update the state in a way that React understands and can track, leading to UI updates.

💡Conditional Rendering

Conditional rendering in React is the process of rendering different components or elements based on certain conditions. The video script demonstrates conditional rendering with a Boolean state variable, where the UI displays 'yes' or 'no' based on whether the variable is true or false. This showcases how React can dynamically change what is displayed on the screen based on state.

💡CSS Styling

CSS styling is used to define the appearance of web elements. In the video, after creating a functional counter component, the presenter applies CSS to style the component. This includes setting font sizes, colors, margins, and other properties to make the counter visually appealing and interactive.

Highlights

Introduction to the useState React hook and its role in functional components.

Explanation of React hooks as a feature introduced in React version 16.8.

Overview of various React hooks including useState, useEffect, useContext, useReducer, useCallback, and more.

Detailed explanation of useState hook for creating stateful variables and setter functions.

Demonstration of how to use useState hook in a functional component.

Importing the useState hook from the React library using object destructuring.

Creating a stateful variable and setter function using array destructuring.

Example of updating the stateful variable using its setter function to trigger a rerender.

Explanation of the difference between stateful variables and normal variables in React.

Creating an initial state for the useState hook.

Incrementing a stateful variable using a function and the setter.

Creating a Boolean stateful variable and toggling its value with a button click.

Conditional rendering based on the stateful variable's value using the ternary operator.

Building a counter program using the useState hook to manage count state.

Creating functions to increment, decrement, and reset the counter state.

Styling the counter program with CSS for better user interface.

Final demonstration of the fully functional counter program with styled buttons and display.

Summary of the useState hook's capabilities and its importance in React functional components.

Transcripts

hey what's going on everybody in today's

video I'm going to explain the usate

react hook and near the end of this

video we're going to create a reactive

counter program so sit back relax and

enjoy the show I haven't explained what

react hooks are yet a react Hook is a

special function that allows functional

components to use react features without

writing class components this was a

change made in react version 16.8

basically we no longer need to write

class components we can write function

based components that use rea hooks to

use react features there are many react

hooks if a function begins with use it's

probably a react hook use State use

effect use context use reducer use

callback and more use state is the most

widely used use state is a react hook

that allows the creation of a stateful

variable and a Setter function to update

its value in the virtual Dom basically

by using the UST State hook we can

create not just a variable but a

stateful variable when you update this

variable that change will be reflected

in the virtual Dom normal variables

don't when you use the UST State hook

you're given a variable and a Setter

function specifically for that variable

so what we'll do in this example is

create a new component going to our

source folder we're going to create a

new file we'll name this component my

component we use react hooks in function

based components so make sure you're not

writing a class

component with this component we will

export it export default my component

then be sure to import this because I'm

probably going to forget if we don't do

it now so we will import my

component from its location

do/ my component and this is a jsx file

let's return one my

component and we are ready to begin in

order to use a react hook we need to

import it it at the top of this

component we will import the react

Library however we don't need the entire

react Library we can use object

destructuring to extract individual

variables or functions I would just like

the UST State function we don't need the

entire react library from its location

react we now have access to this use

State function using the use State

function we'll create a stateful

variable and a set function to update

that variable so let's declare const

we're going to use a set of straight

brackets for array

destructuring equals use State function

the use State function returns an array

with two elements a variable and a

Setter function we're going to use array

destructuring to destructure these two

elements we'll create a stateful

variable for name then we're given a

Setter function specifically for this

variable a common naming convention is

to typee set then the variable name with

camel case naming convention and that's

it if we ever need to change the value

of the stateful variable we have to do

so with this Setter it's a function at

the bottom we're going to

return a

development within this development

we'll create a paragraph element and a

button we'll begin with a paragraph

element that has text of name

and I'm going to zoom in a little bit I

will insert some JavaScript using curly

braces let's display our name following

our paragraph element let's include a

button the button will have an onclick

attribute equal to a JavaScript function

so we need a set of curly braces to

embed that let's create a function to

update name for the text of the button

let's say set name

name all right now we just need to

declare this function I'll use an arrow

function const update name equals Arrow

function so what would we like to do

okay let's attempt to set our name equal

to type your name or some other name I'm

just going to type in

SpongeBob if I click on this button we

should update our name right well that

doesn't appear

work so if I were to

console.log my name

variable then attempt to update it using

this button if I were to go to my

console hold on I'm going to use let so

we can update it if I attempt to change

this name of the

variable it does so within our

console but it doesn't update in react

the virtual Dom is still displaying the

previous state so if I would like to

display display any changes I will want

to use that Setter instead of setting

our name equal to a new value I'm going

to change this back to be a

constant we will use the setter function

and pass in a new value so let me type

in a new

value and that should work we have

updated our name when you use the setter

function of a stateful variable it will

trigger a rerender of the virtual Dom

normal variables don't that's why the US

state Hook is useful we can create a

stateful variable when the stateful

variable gets updated with its Setter

function it triggers a render of the

virtual Dom with the UST State function

you can pass in an initial state

currently we're not passing in anything

for the initial State I will set this to

be

guested when I refresh everything and

start over the initial state is guessed

whatever value you pass in to the UST

State hook then I can set my name again

to something else now we're going going

to create an age variable and increment

it const we're going to use array to

structuring we need a stateful variable

like age and a Setter function for that

age set age equals use

state if you would like an initial value

you can place that within the UST State

function I'll set the initial value of

age to be

zero I'm going to copy this paragraph

and this button

change name to be

age we'll create a function to increment

age the text on the button will

be increment

age now we just need this

function

const increment age I'll use an arrow

function to increment our age we will

use the set age

function let's take our age +

one so our initial value for our age is

zero but every time I click on the

button we will update the value of that

variable so every time I click the

button we're increasing our age by

one or even a different number this time

I'll increase our age by two on each

button click so we start at zero then

we'll increment by two 2 4 6 8 10

now this time we'll create a Boolean

variable and toggle it between being

true and false using the usate hook we

will create const is

employed the setter function will be set

is

employed equals the use State

hook I would like an initial value of

false let's create a paragraph element

and a button

I will set the text of the paragraph to

be is

employed instead of displaying a Boolean

directly let's use the tary operator for

conditional rendering is employed if

that is true we'll display yes otherwise

no when we click on the button let's

create a function

to

toggle toggle employed

status that's kind of a Long Function

name all right let's create a function

const toggle employed status equals an

arrow

function we will use the setter function

set is employed pass in a new value

let's switch this value from being false

to true and true to false every time we

click the button since this is a Boolean

we can use the not logical operator to

reverse it so let's say not is

employed and let's see if this works is

employed no oh let's change the text on

the button

too toggle

status there we go all right when we

click on the button we can toggle this

Boolean from being true to false and

false to true and this should happen

every time I click the

button as a project what we're going to

do now is create a counter program so

let's close out of my

component we'll create a new component

for a counter component counter.

jsx this will be a function base

component

function

counter then be sure to export it export

default

counter going back to our app component

we will import our counter component

from its

location counter. jsx then we will

include one counter component and that's

it in order for us to use the use State

hook we have to import it from the react

Library import react we'll use object

destructuring just to get the US state

hook and nothing else from its location

of

react all we need is one variable a

counter let's say const we'll use array

destructuring create a stateful variable

of count and a Setter function for that

count set count equals the use State

hook would we like an initial value for

count we would like the initial value to

be

zero we'll create a few functions to

increment decrement and reset the

counter const

increment equals I'll use an arrow

function to up update the count to

increment it we will use the set count

function the value we pass in is Count +

one then let's do this for

decrement const decrement count minus

one then

reset const reset for set count we'll

pass in zero to reset the

count now we're going to return some

elements we'll also style this with CSS

let's begin with the div

element I'm going scroll down a little

bit my div element will have a class

name equal to

counter-

container I will create a paragraph

element with a class

name equal to count

display to display the

number for the text of the paragraph I

will insert some JavaScript and display

our count

variable we'll create three buttons for

the first we'll create a button element

this button will have a class

name of

counter-

button the onclick attribute will be set

equal to a JavaScript function this

first button will be the decrement

button for the unclick attribute we will

set this equal to the decrement function

for the text on the button we'll say

decrement and there's our first button

so let's copy this button paste it the

second button will be for reset the text

will be

reset then the third button will be

increment onclick will be the increment

function

the text will be

increment all right and that's all that

we need let's check it for functionality

to be sure that everything works we can

increment this number we can decrement

it and we can reset

it so for the icing on the cake let's

style it with

CSS going to our index CSS stylesheet

we'll apply the following CSS let's

select our counter

container do counter container I will

text align

Center change the font

family I will pick a s serif font of

Ariel with a backup of s

serif next we'll select the count

display select the class of count

display that would be this number will

increase the font size to something

massive like 10 em RM works too okay

that's a little too big but I am zoomed

in actually you know what that's perfect

I will set the margin top to be zero to

close this Gap and I will set the margin

on the bottom to be 50

pixels then let's work on the counter

buttons

next select the class of counter button

I will set the width to be 150 pixels

the height to be 50

pixels the font

size to be 1.5

em I will set the font weight to be

bold set the margin to

be 0 pixels by 5

pixels this would be for the left and

right of the

buttons change the background

color pick a color that you

like I'm going to use hsl values

though that's pretty good I will set the

color of the font to be

white remove the

border border

none set the Border radius to around the

corners five

pixels

and change our cursor to be a pointer if

we hover over the button when we hover

over the button I'm going to change the

background color of the button so with

the counter button class with the

counter button class we will select the

hover sudo class we'll take our

background color decrease the lightness

to be 10%

darker there we

are and that is all the CSS styling that

we need we have our counter program we

can increment the counter we can

decrement it and we can reset

it all right everybody so that is the

use State react hook it allows the

creation of a stateful variable and a

Setter function to update its value in

the virtual Dom when you include the UST

State hook you're given an array of two

elements we use array destructuring to

create a stateful variable and a Setter

function to update that variable and

well everybody that is the UST State

hook in react