i can not react

React Hooks

August 30, 2019

This article is written by ajeasmith

Before I dive into react hooks and functional components, let’s do a quick review on how state is managed within class based components…

import React, { Component } from 'react'

class App extends Component {
    constructor(props){
     super(props)
     
     this.state = {
         count: 0
        } 
    }
    
    counting = () =>{
        let {count} = this.state
        this.setState(count: count++)
    }
    render(){
        return (
            <div>
                count is: {this.state.count}
                <buton onClick={this.counting}>add</button>
            </div>
        )
    }
}

In this class based component we defined what our state of this App component will look like. -> {count: 0} within our this.state object.

We then create a method called “counting” and changed our state using this.setState with our updated value. In our case, the {count: count++} property is incrementing when button is clicked —> <button onClick={this.counting}>add</button>

This is how it is done with class components, let’s talk about functional components now…

Functional Components

Things to note when converting to functional components (NO HOOKS)

  • The ’this’ keyword is no longer available
  • They do not have state or lifecycle methods
  • They’re just pure functions that return something
  • They were known as dummy components because they return the UI, NOT state or logic.

When hooks were created, it changed how functional components operate.

Functional Components with… React hooks

React Hooks -

Functions that allow you to use state and lifecycle methods within functional components.

Functional components (AFTER) react hooks

  • They can have state
  • They can have lifecycle methods

Side note —> however, they still don’t have access to ’this’.

Types of hooks:
  • useState - let’s you add and update state within your functional components.
  • useRef - make a reference to an element.
  • useEffect - method similar to componentDidMount/componentDidUpdate, gets called when component renders/updates.

let’s change that class based component into a functional component with hooks…

import React, { useState } from 'react'

const App (){
    const [count, setCount] = useState(0)
    
    counting = () =>{
        setCount(count++)
    }
    return(
        <div>
            count is: {count}
            <button onClick={counting}>add</button>
        </div>
    )
}

Let’s break down what’s happening here…

  1. We are importing the useState method from react
  2. We are creating a functional component named App
  3. The count and setCount are values we destructer out of the useState. the count is the state and setCount is the function that updates it.
  4. Inside our useState we pass in our initial state, which is 0.
  5. We create a counting method that updates the count using the setCount method.
  6. Lastly, the button calls the counting method and updates the count. we can see the count value by adding it in our return
  7. count is : {count}.

OR…

We can pass in an object for our initial state with multiple properties. Like this —> const [state, setState] = useState({count: 0, isLoading: false}) then we can access our properties in our return using state.count or state.isLoading.

RECAP

  • Don’t have access to ‘this’ keyword
  • React hooks can only be used in functional components
  • There are many types of hooks you can use like useState, useRef, and useEffect.
  • A string, object, number or null can be passed in as the initial state when using useState.