import React from 'react';
import { FlatList, ActivityIndicator, Text, View  } from 'react-native';

export default class FetchExample extends React.Component {

  constructor(props){
    super(props);
    this.state ={ isLoading: true}
  }

  ponentDidMount(){

        fetch('', {
             method: 'GET',
             headers: {
               Accept: 'application/json',
               'Content-Type': 'application/json',
             },
             body: JSON.stringify({
               firstParam: 'isoCode ',
               secondParam: 'internationalCode',
               thirdParam: 'name',
               fourthParam: 'code',
               FifthParam: 'group',
               SixthParam: 'id'
             }),
           });

}


  render(){

    if(this.state.isLoading){
      return(
        <View style={{flex: 1, padding: 20}}>
          <ActivityIndicator/>
        </View>
      )
    }

    return(
      <View style={{flex: 1, paddingTop:20}}>
        <FlatList
          data={this.state.dataSource}
          renderItem={({item}) => <Text>{item.isoCode}, {item.internationalCode}, {item.name}, {item.code}, {item.group}</Text>}
          keyExtractor={({id}, index) => id}
        />
      </View>
    );
  }
}

I am the beginner of react native and i am trying to get data from api but i have an error about code.

possible unhandled promise rejection (id 0) typeerror undefined is not an object

I can't understand why there is no object

Hope for your help.

import React from 'react';
import { FlatList, ActivityIndicator, Text, View  } from 'react-native';

export default class FetchExample extends React.Component {

  constructor(props){
    super(props);
    this.state ={ isLoading: true}
  }

  ponentDidMount(){

        fetch('https://apitest.kuveytturk..tr/prep/v1/data/fecs', {
             method: 'GET',
             headers: {
               Accept: 'application/json',
               'Content-Type': 'application/json',
             },
             body: JSON.stringify({
               firstParam: 'isoCode ',
               secondParam: 'internationalCode',
               thirdParam: 'name',
               fourthParam: 'code',
               FifthParam: 'group',
               SixthParam: 'id'
             }),
           });

}


  render(){

    if(this.state.isLoading){
      return(
        <View style={{flex: 1, padding: 20}}>
          <ActivityIndicator/>
        </View>
      )
    }

    return(
      <View style={{flex: 1, paddingTop:20}}>
        <FlatList
          data={this.state.dataSource}
          renderItem={({item}) => <Text>{item.isoCode}, {item.internationalCode}, {item.name}, {item.code}, {item.group}</Text>}
          keyExtractor={({id}, index) => id}
        />
      </View>
    );
  }
}

I am the beginner of react native and i am trying to get data from api but i have an error about code.

possible unhandled promise rejection (id 0) typeerror undefined is not an object

I can't understand why there is no object

Hope for your help.

• javascript
• android
• react-native

• can you share the entire error which you got? – Gaurav Roy Commented Oct 22, 2019 at 6:39
• i cant add photo about error because of reputation but error is : Possible unhandled promise rejection (id 0) typeerror Body not allowed for GET or HEAD requests – chc Commented Oct 22, 2019 at 6:48
• github./github/fetch/issues/402 check this – Gaurav Roy Commented Oct 22, 2019 at 6:48
• 1 you cant add a body in your get requets, that's what the error is – Gaurav Roy Commented Oct 22, 2019 at 6:49

3 Answers 3

Please note that you cannot use body in GET Request. Please change it to POST.

You can not use body with GET request. If you want to pass params with GET request then the official way to work with query parameters is just to add them onto the URL. This is an example:

var url = new URL("https://apitest.kuveytturk..tr/prep/v1/data/fecs"),
    params = {firstParam: 'isoCode ',
               secondParam: 'internationalCode',
               thirdParam: 'name',
               fourthParam: 'code',
               FifthParam: 'group',
               SixthParam: 'id'}
Object.keys(params).forEach(key => url.searchParams.append(key, params[key]))
fetch(url).then(/* … */)

You can't use body in GET request. Although you can convert your JSON object to URL query parameters like this.

let url += '?'+Object.keys(params).map((k) => (k + '=' + encodeURIComponent(params[k]))).join('&')