How to Bubble Events Through Nested Components in React?

React supports synthetic events in both the capturing and bubbling phases.

Therefore, our click events are propagated to the parent elements unless we stop them from doing so explicitly.

So if we have:

<root>
  <div onClick={this.handleAllClickEvents}>
    <foo>
      <bar>
        <target />
      </bar>
    </foo>
  </div>
</root>

We can listen to click events from child component with the handleAllClickEvents method.

Within it, we can write:

handleAllClickEvents(event) {
  const target = event.relatedTarget;
  const targetId = target.id;
  switch(targetId) {
    case 'foo':
      //...
    case 'bar':
      //...
  }
}

We get the click target with the event.relatedTarget property.

Then we get the click target’s ID with the id property.

Then we can check the IDs as we wish.

Difference Ways to Set the Initial State in a React Class Component

There’re multiple ways to set the initial state of a component in a class.

One way is standard and the other isn’t.

The standard way would be:

class App extends Component {
  constructor(props) {
    super(props);
    this.state = {
      name: 'james'
    }
  }

  render() {
    return  <div>{this.state.name}</div>
  }
}

We set it in the constructor with the this.state assignment.

The non-standard way is:

class App extends Component {
  state = {
    name: 'John'
  }

  render() {
    return  <div>{this.state.name}</div>
  }
}

This isn’t standard JavaScript syntax.

However, we can use it with TypeScript or a Babel plugin to transform it back to standard JavaScript.

This also sets the this.state instance variable.

Pass Props to a Component Passed as a Prop

If we want to pass props to a component that has been passed in as a prop, then we need to clone with the React.cloneElement method.

For instance, we can write:

const GrandChild = props => <div>{props.count}</div>;

class Child extends React.Component{
  constructor(){
    super();
    this.state = { count: 1 };
    this.updateCount= this.updateCount.bind(this);
  }

  updateCount(){
    this.setState(prevState => ({ count: prevState.count + 1 }))
  }

  render(){
    const Comp = this.props.comp;
    return (
      <div>
        {React.cloneElement(Comp, { count: this.state.count })}
        <button onClick={this.updateCount}>+</button>
      </div>
    );
  }
}

class Parent extends React.Component{
  render() {
    return(
      <Child comp={<GrandChild />} />
    )
  }
}

We have the GrandChild component which displays the count prop.

Then we have the Child prop to let us update the count state.

We pass that into the component that’s been passed in from the comp prop with React.cloneElement .

We got to clone it so that we return a version of the component that’s writable.

The 2nd argument has the prop name and value that we want to pass in respectively.