ComponentLifecycle.md

Component Lifecycle

It's important to understand which lifecycle hooks are going to be called on your route components to implement lots of different functionality in your app. The most common thing is fetching data.

There is no difference in the lifecycle of a component in the router as just React itself. Let's peel away the idea of routes, and just think about the components being rendered at different urls.

Consider this route config:

<Route path="/" component={App}>
  <IndexRoute component={Home}/>
  <Route path="invoices/:invoiceId" component={Invoice}/>
  <Route path="accounts/:accountId" component={Account}/>
</Route>

Lifecycle hooks when routing

1. Lets say the user enters the app at /.

   Component	Lifecycle Hooks called
   App	componentDidMount
   Home	componentDidMount
   Invoice	N/A
   Account	N/A

2. Now they navigate from / to /invoice/123

   Component	Lifecycle Hooks called
   App	componentWillReceiveProps, componentDidUpdate
   Home	componentWillUnmount
   Invoice	componentDidMount
   Account	N/A

   • App gets componentWillReceiveProps and componentDidUpdate because it stayed rendered but just received new props from the router (like: children, params, location, etc.)
   • Home is no longer rendered, so it gets unmounted.
   • Invoice is mounted for the first time.

3. Now they navigate from /invoice/123 to /invoice/789

   Component	Lifecycle Hooks called
   App	componentWillReceiveProps, componentDidUpdate
   Home	N/A
   Invoice	componentWillReceiveProps, componentDidUpdate
   Account	N/A

   All the components that were mounted before, are still mounted, they just receive new props from the router.

4. Now they navigate from /invoice/789 to /accounts/123

   Component	Lifecycle Hooks called
   App	componentWillReceiveProps, componentDidUpdate
   Home	N/A
   Invoice	componentWillUnmount
   Account	componentDidMount

Fetching Data

While there are other ways to fetch data with the router, the simplest way is to simply use the lifecycle hooks of your components and keep that data in state. Now that we understand the lifecycle of components when changing routes, we can implement simple data fetching inside of Invoice.

let Invoice = React.createClass({

  getInitialState () {
    return {
      invoice: null
    }
  },

  componentDidMount () {
    // fetch data initially in scenario 2 from above
    this.fetchInvoice()
  },

  componentDidUpdate (prevProps) {
    // respond to parameter change in scenario 3
    let oldId = prevProps.params.invoiceId
    let newId = this.props.params.invoiceId
    if (newId !== oldId)
      this.fetchInvoice()
  },

  componentWillUnmount () {
    // allows us to ignore an inflight request in scenario 4
    this.ignoreLastFetch = true
  },

  fetchInvoice () {
    let url = `/api/invoices/${this.props.params.invoiceId}`
    this.request = fetch(url, (err, data) => {
      if (!this.ignoreLastFetch)
        this.setState({ invoice: data.invoice })
    })
  },

  render () {
    return <InvoiceView invoice={this.state.invoice}/>
  }

})