React / React-Native无法将JSON数据分配给状态变量

Question

I have a state variable ( wallsJSON ) in react-native that is supposed to hold JSON data returned from the URL http://unsplash.it/list

So in my constructor/getInitialState I have the variable set up like this

{
  wallsJSON : []
}

I am using the following function to fetch the json data

  fetchWallsJSON() {
    var url = 'http://unsplash.it/list';
    fetch(url)
      .then( response => response.json())
      .then( jsonData => {
        this.setState({
          isLoading: false,
          wallsJSON: jsonData
        });
      })
      .catch( error => console.log('JSON Fetch error : ' + error) );
  }

I am facing this error :

JSON Fetch error : TypeError: In this environment the target of assign MUST be an object.This error is a performance optimization and not spec compliant.

I tried using underscore to convert the returned data to Object using _.object , also I tried simple wallsJson: Object(jsonData)

but none of which worked.

Answer 1

This works for me. The json I am returning comes after resolving the promise response.json()

function fetch(url) {

  return fetch(url).then(response =>
    response.json().then(json => {
      return json;
    })
  );
}

If the above solution does not work, try the one from the documentation in github/fetch without using es6 arrow function. This should work for sure. We can then try converting the solution below to es6 syntax.

fetch('/users.json')
  .then(function(response) {
    return response.json()
  }).then(function(json) {
    console.log('parsed json', json)
  }).catch(function(ex) {
    console.log('parsing failed', ex)
  })

Answer 2

i think the error is obvious in your fetchWallsJson() function. on the line response => response.json() your'e assing the results to the object json. so the next line should be

.then(json => { this.setState({
   isLoading: true,
   wallsJson: json, //json.results or something likes that(highly likely)          
          }) 
)

//which would be the same object you assinged your response to.