Map function does not return items in React JSX

Question

Outside my PlaylistsLinks component I initialize the folders variable and then I run a Firebase function that iterates through all the folder names and pushes it to the folders array. My map function does not iterate through my folders array even though I can console.log my array within my component. Is there a specific way I have to pass the array into the functional component in order to use map?

import React, { useState, useEffect, useRef } from 'react';
import firebase from "firebase/app";
import storage from "firebase/storage";
import  firebaseConfig from "../dropzone/config";



if (!firebase.apps.length) {
    firebase.initializeApp(firebaseConfig);

 }else {
    firebase.app(); // if already initialized, use that one
 }

let fb_storage = firebase.storage();
let storageRef = fb_storage.ref();  

let rootRef = storageRef.root;

let folders = [];



rootRef.listAll().then(function(res) {
    res.prefixes.forEach(function(folderRef) {
        // console.log(folderRef.name)
        folders.push(folderRef.name)
        
        // All the prefixes under listRef.
        // You may call listAll() recursively on them.
    });
    res.items.forEach(function(itemRef) {
        // All the items under listRef.
        // console.log(itemRef.name);
    });
    }).catch(function(error) {
    // Uh-oh, an error occurred!
    }); 

   

const PlayListLinks = () =>{
    
   
console.log(folders);

    return(
        <>
            <ul>
                {folders.map((folder, index) => {
                    return <li key={index}> {folder}</li>
                })}
            </ul>
        </>
    )
}

export default PlayListLinks

Does this answer your question? [How do I return the response from an asynchronous call?](https://stackoverflow.com/questions/14220321/how-do-i-return-the-response-from-an-asynchronous-call) — Randy Casburn, Dec 15 '20 at 20:46
you'll need to implement one of the hooks to update `folders` so that it is rendered. — Randy Casburn, Dec 15 '20 at 20:48
are you able to check the value of `foldeRef` within the `prefixes.forEach` to know if the object even exist and has the object structure you expect? I'd put a debugger and inspect — AGE, Dec 15 '20 at 20:51

score 2 · Accepted Answer · answered Dec 15 '20 at 20:51

create a state and then update it with fetched folder list:

import React, { useState, useEffect, useRef } from 'react';
import firebase from "firebase/app";
import storage from "firebase/storage";
import  firebaseConfig from "../dropzone/config";

if (!firebase.apps.length) {
    firebase.initializeApp(firebaseConfig);

 }else {
    firebase.app(); // if already initialized, use that one
 }

let fb_storage = firebase.storage();
let storageRef = fb_storage.ref();  

let rootRef = storageRef.root;

const PlayListLinks = () =>{
const [folders, setFolders] = useState([])

useEffect(()=>{
    rootRef.listAll().then(function(res) {
    let temp = []
    res.prefixes.forEach(function(folderRef) {
        temp.push(folderRef.name)
    });
    setFolders(temp);
    res.items.forEach(function(itemRef) {
        // All the items under listRef.
        // console.log(itemRef.name);
    });
    }).catch(function(error) {
    // Uh-oh, an error occurred!
    }); 

},[])
   
console.log(folders);

    return(
        <>
            <ul>
                {folders.map((folder, index) => {
                    return <li key={index}> {folder}</li>
                })}
            </ul>
        </>
    )
}

export default PlayListLinks

Beautiful. This works. I had also tried using useEffect but I was doing it wrong. Thank you. — oxxi, Dec 15 '20 at 21:07

score 0 · Answer 2 · answered Dec 15 '20 at 20:55

0

The problem is you have to return your JSX directly from the function within .map

Like so:

{folders.map((folder, index) => <li key={index}>{folder}</li>)}

or:

{folders.map((folder, index) => (
    <li key={index}>{folder}</li>
)}

answered Dec 15 '20 at 20:55

GoodStuffing123

172
10

Map function does not return items in React JSX

2 Answers2