| import React from 'react'; | |
| // Every React component exposes special methods that allow you to plug in logic | |
| // when certain events occur during the component's life. They are called | |
| // 'lifecycle methods', and they can be used in variety of ways. | |
| // They are used mostly to integrate non-React code manipulating the DOM with | |
| // your components - like autocomplete, jQuery plugins etc. | |
| // | |
| // There are three methods that are widely used: | |
| // * componentDidMount - this method fires when React component is rendered for | |
| // the first time in the web browser. It does not run when | |
| // you render component using server-side rendering. | |
| // A render can be caused by an explicit React.render | |
| // call or when a child component is rendered within a render | |
| // method of its parent component. | |
| // | |
| // * componentDidUpdate - this method fires when a component is updated - | |
| // when state changes or the forceUpdate method | |
| // is called explicitly. | |
| // | |
| // * componentWillUnmount - this method fires before the component 'dies'. You | |
| // can unmount the component directly using the | |
| // React.unmountComponentAtNode method. A component can | |
| // be also unmounted during re-rendering of the parent component. | |
| // | |
| // Tasks for this exercise are in comments inside the component class code. | |
| // | |
| // In this exercise lifecycle methods will be used to provide convenient debug | |
| // messages in developer's console. | |
| // There are more lifecycle methods available. | |
| // Those three presented are commonly used. | |
| // | |
| // Extra task: Learn about componentWillUpdate. What's the difference between | |
| // this and the componentDidUpdate method? Think about the possible | |
| // use cases of this lifecycle method. | |
| // Extra task: Learn about componentWillMount. How can it be useful? | |
| // (Hint: Think about server-side rendering of React components) | |
| // Extra task: Learn about componentWillReceiveProps. How it can be used? | |
| // Is it fired when you render a component for the first time? | |
| // Extra task: There is a method which directly modifies behavior of React | |
| // itself - it's called shouldComponentUpdate. | |
| // How can you use it to optimise rendering cycle of your | |
| // React components? Learn about PureRenderMixin. | |
| // | |
| // All lifecycle methods are described here: | |
| // http://facebook.github.io/react/docs/component-specs.html | |
| class LifecycleMethodsComponent extends React.Component { | |
| constructor(props) { | |
| super(props); | |
| this.state = { name: "Bob" }; | |
| } | |
| // This code will be called when the component finishes mounting | |
| // (so it is visible for a user). | |
| componentDidMount() { | |
| // Task 1: Display a message "I'm mounted!" in developer's console when the | |
| // component finishes mounting. | |
| // Use `console.log` function for it. | |
| } | |
| componentDidUpdate(prevProps, prevState) { | |
| // Task 2: Display a message "Updated!" in developer's console | |
| // when the component updates. | |
| // Here you also need to use the console.log function. | |
| // Notice that in this lifecycle method you have an access | |
| // to previous values of properties and state. | |
| // Think about it: Could you find a possible use case | |
| // for using previous state and properties values? | |
| } | |
| componentWillUnmount() { | |
| // Task 3: Display a message "Goodbye, cruel world! :(" in developer's | |
| // console when the component unmounts. | |
| // In the real world this lifecycle method is often used to | |
| // 'clean up' external integrations from the component. | |
| // Think about the use case like this: You have an event bus and | |
| // you are listening for events. Your event listeners use setState | |
| // directly. What will happen if you unmount the component? | |
| // How can this lifecycle method help you to avoid such problems? | |
| } | |
| render() { | |
| return (<p>Whatever, {this.state.name}!</p>); | |
| } | |
| } | |
| export default LifecycleMethodsComponent; | |