Class Name is not changing upon changed value in React [duplicate]

Background

I am trying to get familiar with React by creating a To Do App, using the React documentation.

Side note, I am using classes as components rather than functions.

Problem

When a value (this.props.completed) is changed, the className should also change, depending on the completed status. But in my current situation – it’s not updating the className and I can’t figure out why.

Logic:

'completed == true' then set the className = 'taskCompleted'
'completed == false' then set the className = 'taskNotCompleted'

Below is the app, both <div /> elements has class names set to taskNotCompleted, whilst the completed status is set to false, as shown in red on the left hand side of the image:

Next…

Clicking the done button for the 1st task, the completed status is changed as shown in the image below in blue border. But the className has not changed (red border).

this is my Task Class:

class Task extends React.Component {
  constructor(props) {
    super(props);
  }

  render() {
    const isCompleted = this.props.completed;
    return (
      <div className={`task ${isCompleted == true ? 'taskCompleted' : 'taskNotCompleted'}`}>
        <h2>{this.props.title}</h2>
        <p>{this.props.description}</p>
        <button onClick={this.props.handleChange}>Done</button>
        <p>{this.props.completed}</p>
        <p></p>
      </div>
    )
  }
}

I have found this resource: https://stackoverflow.com/a/35225464/12485722 I noticed within the answer, my className is very similar to the answer. Still no ideas why it’s going wrong.

Full Code

class App extends React.Component {
  render() {
    return (
      <Tasks />
    )
  }
}

class Tasks extends React.Component {
  constructor(props) {
    super(props);

    const tasksList = [{
      id: 1,
      title: "Title 1",
      description: "description 1",
      completed: false
    }, {
      id: 2,
      title: "Title 2",
      description: "description 2",
      completed: false
    }]

    this.state = {
      tasks: tasksList
    }

    this.alterStatus = this.alterStatus.bind(this);
  }

  alterStatus(id) {
    const tasks = Object.assign([], this.state.tasks);
    tasks.forEach(element => {
      if (element.id == id) {
        element.completed = true;
      }
    });
    this.setState({ tasks: tasks });
  }

  render() {
    return (
      <div>
        {this.state.tasks.map((task) =>
          <Task
            key={task.id}
            title={task.title}
            description={task.description}
            completed={task.completed.toString()}
            handleChange={() => this.alterStatus(task.id)} />
        )}
      </div>
    )
  }
}

class Task extends React.Component {
  constructor(props) {
    super(props);
  }

  render() {
    const isCompleted = this.props.completed;
    return (
      <div className={`task ${isCompleted == true ? 'taskCompleted' : 'taskNotCompleted'}`}>
        <h2>{this.props.title}</h2>
        <p>{this.props.description}</p>
        <button onClick={this.props.handleChange}>Done</button>
        <p>{this.props.completed}</p>
        <p></p>
      </div>
    )
  }
}

export default App;