Learn All Hooks in React In One tutorials

Hooks are a new addition in React 16.8. They let you use state and other React features without writing a class. Today we'll learn about the widely used hooks in React. First, let me tell you the need for hooks. As we all know React has functional and class components. Previously, the functional components were only used to render the data but didn't consist of the business logic or any side effect in itself.

So hooks were introduced to implement life cycle methods and states in functional components. They also bought the idea of code re-usability along with them, that's why it was so quickly accepted within the React Community.

Why Hooks ?#

We know that components and top-down data flow help us organize a large UI into small, independent, reusable pieces. However, we often can’t break complex components down any further because the logic is stateful and can’t be extracted to a function or another component. Sometimes that’s what people mean when they say React doesn’t let them “separate concerns.”

These cases are very common and include animations, form handling, connecting to external data sources, and many other things we want to do from our components. When we try to solve these use cases with components alone, we usually end up with:

Huge components that are hard to refactor and test. Duplicated logic between different components and life cycle methods. Complex patterns like render props and higher-order components.

We think Hooks are our best shot at solving all of these problems. Hooks let us organize the logic inside a component into reusable isolated units

Drum rolls 🥁

Let's move ahead with the main topic.

useState Hooks ♻️#

This hook helps us to use and maintain a state within the functional component. It's very easy to use. The useState hook returns an array having two elements, the first one is the state variable and the second is the function that modifies the state variable.

import { useState } from "react";

export default function App() {
  const [number, setNumber] = useState(0);

  return (
    <div className="App">
      <button onClick={() => setNumber(number - 1)}>Subtract</button>
      <input
        type="number"
        value={number}
        onChange={(e) => setNumber(e.target.value)}
      />
      <button onClick={() => setNumber(number + 1)}>Add</button>
    </div>
  );
}

Here, we have number as the state variable and setNumber as the function which will modify the number.

Number return the value in current state just like we use the number in input tag in above code.

setNumber is a function which is responsible to set value in the state any value that you pass as argument in the function is going in the state and component is going to re render and the value of number is updated. to learn more read React Blog

useEffect hook ✋#

This hook works as a replacement for all the lifecycle methods which were used in class components. It contains a callback and a dependencies array. The hook will run every time when any of the values in the dependencies array changes.

import { useEffect, useState } from "react";

export default function App() {
  const [number, setNumber] = useState(0);
  const [isEven, toggleEven] = useState(true);

  useEffect(() => {
    if (number % 2 !== 0) {
      toggleEven(false);
    } else {
      toggleEven(true);
    }
  }, [number]);

  return (
    <div className="App">
      <button onClick={() => setNumber(number - 1)}>Subtract</button>
      <input
        type="number"
        value={number}
        onChange={(e) => setNumber(e.target.value)}
      />
      <button onClick={() => setNumber(number + 1)}>Add</button>
      <p>{isEven ? "Even" : "Odd"}</p>
    </div>
  );
}

this hooks run after component is mount on UI

Here as you can see, the dependencies array contains number. So every time the user presses any of the buttons or changes the input value, the useEffect hook will trigger and it'll check the number whether it's odd or even.

Within this hook, you can call side effects such as changing something in DOM, fetching data from an API, etc.

One more thing used in this hook is the cleanup function, which runs when we return a function in the callback. This function helps in cleaning of side effects i.e clearing a timer, closing a web socket, etc.

useContext hook 🍡#

As in the class components, we had the Context API in the same way, we have useContext hook in functional components. This hook basically helps you to maintain a common global state across components. When the state changes it triggers re-renders across all the child components under the Context, even if the parent component uses shouldComponentUpdate or React.memo.

This hook can be used to implement a loading state within the application, passing data to children components, etc.

To create it, we use the createContext function and pass the initial value. In the context provider, we pass a prop called value which consists of the context variables and functions to modify the context.

import { createContext } from "react";

export const UserContext = createContext({
  name: "Initial Name",
});

Then we use this context in our Parent Component and wrap our app inside the Context Provider and pass a value. So now all the child components have the access to the value prop.

import { useContext, useState } from "react";
import Person from "./Person";
import { UserContext } from "./Context";

export default function App() {
  const user = useContext(UserContext);

  const [person, togglePerson] = useState(user);

  return (
    <UserContext.Provider value={[person, togglePerson]}>
      <div className="App">Hello {user.name}!</div>
      <Person />
    </UserContext.Provider>
  );
}

Now in the child component Person we can access the value prop and we can change the context value too.

import { useContext } from "react";
import { UserContext } from "./Context";

function Person() {
  const [person, togglePerson] = useContext(UserContext);

  return (
    <div>
      Person: {person.name}
      <button
        onClick={() => {
          togglePerson({ name: "Stuart Little" });
        }}
      >
        Change
      </button>
    </div>
  );
}

export default Person;

This way you can use the useContext hook. Make a context, wrap the parent component with the context's provider and you are good to go!

You can experiment with the above code here.

useReducer hook 🧪#

If you know Redux then you already what this hook does, if not then simply it changes the state according to the action passed. It helps in maintaining a local state easily whereas in Redux we can do that globally.

To use the reducer globally, we can make a context and pass it across the components. Geddit!

Here we have an initial state and a dispatch to modify the state. Within the dispatch, we pass actions along with some info called payload. The action then goes to the reducer which in turn changes the state.

import { useReducer } from "react";
import "./styles.css";

const initialState = [
  {
    name: "Mad Angles",
    quantity: 5,
  },
  {
    name: "Pringles",
    quantity: 3,
  },
  {
    name: "Lays",
    quantity: 2,
  },
  {
    name: "Kurkure",
    quantity: 1,
  },
  {
    name: "Uncle Chips",
    quantity: 9,
  },
];

function reducer(state, action) {
  switch (action.type) {
    case "add":
      return [...state, action.payload];
    case "delete":
      return state.filter((_, index) => index !== action.payload);
    default:
      return state;
  }
}

export default function App() {
  const [state, dispatch] = useReducer(reducer, initialState);

  return (
    <div className="App">
      <h1>Hello CodeSandbox</h1>
      <ul>
        {state.map(({ name, quantity }, index) => (
          <div className="list-item">
            <li key={name}>
              <b>{name}</b> - {quantity}
            </li>
            <button
              onClick={() => {
                dispatch({ type: "delete", payload: index });
              }}
            >
              delete
            </button>
          </div>
        ))}
        <button
          onClick={() => {
            dispatch({
              type: "add",
              payload: {
                name: "Doritoes",
                quantity: 5,
              },
            });
          }}
        >
          add
        </button>
      </ul>
    </div>
  );
}

You can find the above code here.

That's it for now. There are other hooks too like useRef, useCallback but they are rarely used.

useCallback 📞#

const memoizedCallback = useCallback(() => {
  doSomething(a, b);
}, [a, b]);

Returns a memoized callback.

Pass an inline callback and an array of dependencies. useCallback will return a memoized version of the callback that only changes if one of the dependencies has changed. This is useful when passing callbacks to optimized child components that rely on reference equality to prevent unnecessary renders (e.g. shouldComponentUpdate).

useCallback(fn, deps) is equivalent to useMemo(() => fn, deps).

usememo#

const memoizedValue = useMemo(() => computeExpensiveValue(a, b), [a, b]);

Returns a memoized value.

Pass a “create” function and an array of dependencies. useMemo will only recompute the memoized value when one of the dependencies has changed. This optimization helps to avoid expensive calculations on every render.

Remember that the function passed to useMemo runs during rendering. Don’t do anything there that you wouldn’t normally do while rendering. For example, side effects belong in useEffect, not useMemo.

If no array is provided, a new value will be computed on every render.

You may rely on useMemo as a performance optimization, not as a semantic guarantee. In the future, React may choose to “forget” some previously memoized values and recalculate them on next render, e.g. to free memory for offscreen components. Write your code so that it still works without useMemo — and then add it to optimize performance.

useref#

const refContainer = useRef(initialValue);

useRef returns a mutable ref object whose .current property is initialized to the passed argument (initialValue). The returned object will persist for the full lifetime of the component.

A common use case is to access a child imperatively:

function TextInputWithFocusButton() {
  const inputEl = useRef(null);
  const onButtonClick = () => {
    // `current` points to the mounted text input element
    inputEl.current.focus();
  };
  return (
    <>
      <input ref={inputEl} type="text" />
      <button onClick={onButtonClick}>Focus the input</button>
    </>
  );
}

Essentially, useRef is like a “box” that can hold a mutable value in its .current property.

You might be familiar with refs primarily as a way to access the DOM. If you pass a ref object to React with <div ref={myRef} />, React will set its .current property to the corresponding DOM node whenever that node changes.

However, useRef() is useful for more than the ref attribute. It’s handy for keeping any mutable value around similar to how you’d use instance fields in classes.

This works because useRef() creates a plain JavaScript object. The only difference between useRef() and creating a {current: ...} object yourself is that useRef will give you the same ref object on every render.

Keep in mind that useRef doesn’t notify you when its content changes. Mutating the .current property doesn’t cause a re-render. If you want to run some code when React attaches or detaches a ref to a DOM node, you may want to use a callback ref instead.

useimperativehandle#

useImperativeHandle(ref, createHandle, [deps]);

useImperativeHandle customizes the instance value that is exposed to parent components when using ref. As always, imperative code using refs should be avoided in most cases. useImperativeHandle should be used with forwardRef:

function FancyInput(props, ref) {
  const inputRef = useRef();
  useImperativeHandle(ref, () => ({
    focus: () => {
      inputRef.current.focus();
    }
  }));
  return <input ref={inputRef} ... />;
}
FancyInput = forwardRef(FancyInput);

In this example, a parent component that renders <FancyInput ref={inputRef} /> would be able to call inputRef.current.focus().

uselayouteffect#

The signature is identical to useEffect, but it fires synchronously after all DOM mutations. Use this to read layout from the DOM and synchronously re-render. Updates scheduled inside useLayoutEffect will be flushed synchronously, before the browser has a chance to paint.

Prefer the standard useEffect when possible to avoid blocking visual updates.

usedebugvalue#

useDebugValue(value);

useDebugValue can be used to display a label for custom hooks in React DevTools.

For example, consider the useFriendStatus custom Hook described in “Building Your Own Hooks”:

function useFriendStatus(friendID) {
  const [isOnline, setIsOnline] = useState(null);

  // ...

  // Show a label in DevTools next to this Hook  // e.g. "FriendStatus: Online"
  //  useDebugValue(isOnline ? 'Online' : 'Offline');
  return isOnline;
}

thank you to read this article i hope your all dough are clean if any thing i missed then please inform me at twitter otherwise please contribute your suggestion on github