freeCodeCamp

3.7 KiB

Raw Blame History

id	title	challengeType	isRequired	forumTopicId
5a24c314108439a4d4036170	Create a Stateful Component	6	false	301391

Description

One of the most important topics in React is state. State consists of any data your application needs to know about, that can change over time. You want your apps to respond to state changes and present an updated UI when necessary. React offers a nice solution for the state management of modern web applications. You create state in a React component by declaring a state property on the component class in its constructor. This initializes the component with state when it is created. The state property must be set to a JavaScript object. Declaring it looks like this:

this.state = {
  // describe your state here
}

You have access to the state object throughout the life of your component. You can update it, render it in your UI, and pass it as props to child components. The state object can be as complex or as simple as you need it to be. Note that you must create a class component by extending React.Component in order to create state like this.

Instructions

There is a component in the code editor that is trying to render a name property from its state. However, there is no state defined. Initialize the component with state in the constructor and assign your name to a property of name.

Tests

tests:
  - text: <code>StatefulComponent</code> should exist and render.
    testString: assert((function() { const mockedComponent = Enzyme.mount(React.createElement(StatefulComponent)); return mockedComponent.find('StatefulComponent').length === 1; })());
  - text: <code>StatefulComponent</code> should render a <code>div</code> and an <code>h1</code> element.
    testString: assert((function() { const mockedComponent = Enzyme.mount(React.createElement(StatefulComponent)); return mockedComponent.find('div').length === 1 && mockedComponent.find('h1').length === 1; })());
  - text: The state of <code>StatefulComponent</code> should be initialized with a property <code>name</code> set to a string.
    testString: assert((function() { const mockedComponent = Enzyme.mount(React.createElement(StatefulComponent)); const initialState = mockedComponent.state(); return ( typeof initialState === 'object' && typeof initialState.name === 'string'); })());
  - text: The property <code>name</code> in the state of <code>StatefulComponent</code> should render in the <code>h1</code> element.
    testString: assert((function() { const mockedComponent = Enzyme.mount(React.createElement(StatefulComponent)); const initialState = mockedComponent.state(); return mockedComponent.find('h1').text() === initialState.name; })());

Challenge Seed


class StatefulComponent extends React.Component {
  constructor(props) {
    super(props);
    // initialize state here

  }
  render() {
    return (
      <div>
        <h1>{this.state.name}</h1>
      </div>
    );
  }
};

After Test

ReactDOM.render(<StatefulComponent />, document.getElementById('root'))

Solution

class StatefulComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      name: 'freeCodeCamp!'
    }
  }
  render() {
    return (
      <div>
        <h1>{this.state.name}</h1>
      </div>
    );
  }
};

3.7 KiB Raw Blame History