ReactJS：未捕获的TypeError：无法读取未定义的属性“ setState”

Question

I'm currently trying to build a small weather app in reactJS (the one for freecodecamp)

currently I'm getting the error: "Uncaught TypeError: Cannot read property 'setState' of undefined"

here is a link to the codepen: http://codepen.io/rasmus/pen/aNGRJm

and here is the code that's the problem I guess:

  componentDidMount: () => {
    if (navigator.geolocation) {
      navigator.geolocation.getCurrentPosition((position) => {
        $.ajax({
          url: URL + "lat=" + position.coords.latitude + "&lon=" + position.coords.longitude + "&APPID=" + APIKEY,
          success: (data) => {
            this.setState({data: data})
          }
        });
      })   
    }
  },

the url is not the problem. I can log the data I'm receiving to the console.

I guess it's because of the scope of this ..

any ideas?

EDIT: I don't think that this is a duplicate because I'm only using arrow functions and they are making .bind(this) obsolete

Answer 1

The callback in your ajax function is called not from within your function, so the this is not pointing to what you expect, ie, your class.

Save a reference and use it from there:

componentDidMount: () => {
    if (navigator.geolocation) {
      navigator.geolocation.getCurrentPosition((position) => {
        let self = this;
        $.ajax({
          url: URL + "lat=" + position.coords.latitude + "&lon=" + position.coords.longitude + "&APPID=" + APIKEY,
          success: (data) => {
            self.setState({data: data})
          }
        });
      })   
    }
  },

Answer 2

Try to use arrow function like follows in componentDidMount:

componentDidMount = () => {
    if (navigator.geolocation) {
      navigator.geolocation.getCurrentPosition((position) => {
        let self = this;
        $.ajax({
          url: URL + "lat=" + position.coords.latitude + "&lon=" + position.coords.longitude + "&APPID=" + APIKEY,
          success: (data) => {
            self.setState({data: data})
          }
        });
      })   
    }
}

You need to cache the reference to this outside of that API call. The arrow function binds this for you so you can access it within the function and it will still point to the component.