react functional component state and lifecycle methods code example

Example 1: how to use componentdidmount in functional component

// passing an empty array as second argument triggers the callback in useEffect
// only after the initial render thus replicating `componentDidMount` lifecycle behaviour
useEffect(() => {
  if(!props.fetched) {
 	 props.fetchRules();
  }
  console.log('mount it!');
}, []);

// componentDidUpdate
useEffect({
	your code here
}) 

// For componentDidUpdate
useEffect(() => {
  // Your code here
}, [yourDependency]);

// For componentWillUnmount
useEffect(() => {
  // componentWillUnmount
  return () => {
     // Your code here
  }
}, [yourDependency]);

Example 2: react lifecycle hooks

class ActivityItem extends React.Component {
  render() {
    const { activity } = this.props;

    return (
      <div className='item'>
        <div className={'avatar'}>
          <img
            alt='avatar'
            src={activity.actor.avatar_url} />
        </div>

        <span className={'time'}>
          {moment(activity.created_at).fromNow()}
        </span>
        
        <p>{activity.actor.display_login} {activity.payload.action}</p>
        <div className={'right'}>
          {activity.repo.name}
        </div>
      </div>
    )
  }
}