Answers for "react all hooks"

useRef

/*
	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>
    </>
  );
}

hooks in react

import React, { useState, useEffect } from "react";
export default props => {
  console.log("componentWillMount");
  console.log("componentWillReceiveProps", props);
  const [x, setX] = useState(0);
  const [y, setY] = useState(0);
  const [moveCount, setMoveCount] = useState(0);
  const [cross, setCross] = useState(0);
  const mouseMoveHandler = event => {
    setX(event.clientX);
    setY(event.clientY);
  };
  useEffect(() => {
    console.log("componentDidMount");
    document.addEventListener("mousemove", mouseMoveHandler);
    return () => {
      console.log("componentWillUnmount");
      document.removeEventListener("mousemove", mouseMoveHandler);
    };
  }, []); // empty-array means don't watch for any updates
  useEffect(
    () => {
      // if (componentDidUpdate & (x or y changed))
      setMoveCount(moveCount + 1);
    },
    [x, y]
  );
useEffect(() => {
    // if componentDidUpdate or componentDidMount
    if (x === y) {
      setCross(x);
    }
  });
  return (
    <div>
      <p style={{ color: props.color }}>
        Your mouse is at {x}, {y} position.
      </p>
      <p>Your mouse has moved {moveCount} times</p>
      <p>
        X and Y positions were last equal at {cross}, {cross}
      </p>
    </div>
  );
};

how to use hooks react

const App = () => {
const [students , setStudents] = useState([]);
  
  return (
// put in the jsx code here
  )
}

react hooks

class Example extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0
    };
  }

  componentDidMount() {    document.title = `You clicked ${this.state.count} times`;  }  componentDidUpdate() {    document.title = `You clicked ${this.state.count} times`;  }
  render() {
    return (
      <div>
        <p>You clicked {this.state.count} times</p>
        <button onClick={() => this.setState({ count: this.state.count + 1 })}>
          Click me
        </button>
      </div>
    );
  }
}