deek deek - 4 months ago 18
Javascript Question

Why is my react component not updating with state updates?

I have a map app I built that requires some map icons to appear/disappear after a button press, but I can't figure out how to set it to re-render the component when I pass in a new sports property from it's parents component :

Parent loads component:

<SimpleMap sports=[default value and future values go here] />


Simple map component(simplified):

constructor(props) {
(props);
this.state = {
events: [{venue: {lat: 2, lon: 1}}],
sports: ["baseball", "football", "paddle", "soccer", "boxing", "dart", "biking", "golf", "hockey", "inline-skating", "tennis", "volleyball", "skateboard", "kickball", "bowling", "pool", "ride", "hike", "ice-skating"]
};
};

componentWillReceiveProps (nextProps) {
this.setState({events: [{venue: {lat: 2, lon: 1}}],
sports: nextProps.sports});
console.log(nextProps.sports);
}

static defaultProps = {
center: {lat: 36.160338, lng: -86.778780},
zoom: 12,
sports: ["baseball", "football", "paddle", "soccer", "boxing", "dart", "biking", "golf", "hockey", "inline-skating", "tennis", "volleyball", "skateboard", "kickball", "bowling", "pool", "ride", "hike", "ice-skating"],
};

makeMapEvents (insertProps) {
fetch("./json/meetup.json").then((response) => {
return response.json()
}).then((response) => {
/* eventually returns new events object based on insertProps */
this.setState({events: response});
}
};

componentDidMount () {
this.makeMapEvents(this.state.sports);
console.log("mounted", this.state.sports);
}


Eventually ends up here to map events from state:

<GoogleMap>
{this.state.events.map((result) => {
return (<Marker key={counter++} lat={result.venue.lat} lng={result.venue.lon}
sport={this.props.sport} data={result}/>);
})}
</GoogleMap>

Answer

React ES6 classes do not autobind this by default to non-react base member methods. Therefore, the context for this in your function makeMapEvents is not bound correctly. There are 2 ways to fix this:

Via ES7 property initializer:

makeMapEvents = (insertProps) => {
  fetch("./json/meetup.json").then((response) => {
    return response.json()
  }).then((response) => {
    /* eventually returns new events object based on insertProps */
    this.setState({events: response});
  })
};

Via binding in constructor:

constructor(props) {
  (props);
  this.state = {
    events: [{venue: {lat: 2, lon: 1}}],
    sports: ["baseball", "football",  "paddle", "soccer", "boxing", "dart", "biking", "golf", "hockey", "inline-skating", "tennis", "volleyball", "skateboard", "kickball", "bowling", "pool", "ride", "hike", "ice-skating"]
  };

  this.makeMapEvents = this.makeMapEvents.bind(this) // << important line


}