useContext unused vars react hooks code example

Example 1: 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>
  );
};

Example 2: casl react

import { AbilityBuilder } from '@casl/ability';
import React, { useState, useContext } from 'react';
import { AbilityContext } from './Can';

function updateAbility(ability, user) {
  const { can, rules } = new AbilityBuilder();

  if (user.role === 'admin') {
    can('manage', 'all');
  } else {
    can('read', 'all');
  }

  ability.update(rules);
}

export default () => {
  const [username, setUsername] = useState('');
  const [password, setPassword] = useState('');
  const ability = useContext(AbilityContext);
  const login = () => {
    const params = {
      method: 'POST',
      body: JSON.stringify({ username, password })
    };
    return fetch('path/to/api/login', params)
      .then(response => response.json())
      .then(({ user }) => updateAbility(ability, user));
  };

  return (
    <form>
      {/* input fields */}
      <button onClick={login}>Login</button>
    </form>
  );
};