how to fetch nested array object inside array object in react native

According to the problem, your JSON array has 4 objects but only 3 of them have nested array called resultlist & 1 object hasn't.

{
    "img": "https://www.act.com/image/catalog/cmsblock/Powerbank10.jpg",
    "product_id": 187,
    "sort_order": 1,
    "status": true,
    "type": "middleimage",
}

That's cause error undefined is not an object (evaluating 'item.resultlist.map') because you need an array in order to used map in JS. But that object hasn't resultlist.

That is something you need to handle from the backend. If not you can filtered that object or change structure of that object by adding resultlist:[] as below.

import * as React from "react";
import { Text, View, StyleSheet } from "react-native";

export default class App extends React.Component {
  state = {
    data: [
      {
        resultlist: [
          {
            img:
              "https://www.act.com/image/cache/catalog/new%20thumbnails/Mifa%20A1BlacjkThumbnail-600x600.jpg",
            name: "Mifa F1",
            product_id: 87,
            type: "product"
          },
          {
            category_id: 20,
            img: "https://www.achhacart.com/image/catalog/cmsblock/hgb5.png",
            name: "Earphone",
            type: "category"
          },
          {
            img: "https://www.achhacart.com/image/catalog/cmsblock/air.gif",
            name: "Air Purifier",
            product_id: 87,
            type: "product"
          },
          {
            img:
              "https://www.achhacart.com/image/catalog/cmsblock/Powerbank10.jpg",
            name: "Powerbank",
            product_id: 87,
            type: "product"
          }
        ],
        sort_order: 0,
        status: true,
        type: "product"
      },
      {
        img: "https://www.act.com/image/catalog/cmsblock/Powerbank10.jpg",
        product_id: 187,
        sort_order: 1,
        status: true,
        type: "middleimage"
      },
      {
        resultlist: [
          {
            img:
              "https://www.act.com/image/cache/catalog/new%20thumbnails/Mifa%20A1BlacjkThumbnail-600x600.jpg",
            name: "Mifa A1 Black",
            product_id: 87,
            type: "product"
          },
          {
            category_id: 20,
            img: "https://www.act.com/image/catalog/cmsblock/hgb5.png",
            name: "Earphones",
            type: "category"
          },
          {
            img: "https://www.act.com/image/catalog/cmsblock/air.gif",
            name: "Air Purifiers",
            product_id: 87,
            type: "product"
          },
          {
            img: "https://www.act.com/image/catalog/cmsblock/Powerbank10.jpg",
            name: "Powerbanks",
            product_id: 87,
            type: "product"
          }
        ],
        sort_order: 2,
        status: true,
        type: "product"
      },
      {
        resultlist: [
          {
            image:
              "https://www.act.com/simage/catalog/1AA/WeChatImage_20191228151402.jpg",
            link: "",
            title: "slider1"
          },
          {
            image:
              "https://www.act.com/staging-achhamall.com/image/catalog/1accc/WeChatImage_20191231125513.jpg",
            link: "",
            title: "slider2"
          }
        ],
        sort_order: 3,
        status: true,
        type: "slider"
      }
    ]
  };

  render() {
    let newArray = this.state.data.filter(obj => obj.resultlist);
    return (
      <View style={styles.container}>
        {newArray.map((item, i) => (
          <View>
            <Text key={i} style={{color: 'red'}}>{item.type}</Text>
            {item.resultlist.map((sub, index) => (
              <Text key={index}>{sub.name}</Text>
            ))}
          </View>
        ))}
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: "#ecf0f1",
    padding: 8
  }
});

Hope this helps you. Feel free for doubts