Express - 初始化前无法访问“数据库”

Question

const express = require('express');
const upload = require("express-fileupload");
const editJsonFile = require("edit-json-file");
const fs = require('fs');
const app = express();
app.use(upload())
app.use(express.urlencoded({ extended: true }))
const playlist = editJsonFile(`${__dirname}/playlist.json`);

app.post("/upload", (req, res) => {
    //Save file from the html form to ./mp3
    var file = req.files.file;
    req.pipe(fs.createWriteStream("./mp3/" + file.name));
    res.send("File uploaded");
    playlist.append("playlist", file.name)
    playlist.save()
}),

app.get("/playlist", (req, res) => {
    console.log(playlist.get("playlist"))
    let playlist = playlist.get("playlist")
    let html = "";
    for (let i = 0; i < playlist.length; i++) {
        html += `<br>${playlist[i]}`;
    }
    res.send(html);
}),

嘿，我正在尝试制作音乐播放器，但不知何故我得到了错误：

ReferenceError: Cannot access 'playlist' before initialization
    at C:\Users\Jakob\Documents\Bots\API\PiMusicPlayerV2\index.js:20:17
    at Layer.handle [as handle_request] (C:\Users\Jakob\Documents\Bots\API\PiMusicPlayerV2\node_modules\express\lib\router\layer.js:95:5)
    at next (C:\Users\Jakob\Documents\Bots\API\PiMusicPlayerV2\node_modules\express\lib\router\route.js:144:13)
    at Route.dispatch (C:\Users\Jakob\Documents\Bots\API\PiMusicPlayerV2\node_modules\express\lib\router\route.js:114:3)
    at Layer.handle [as handle_request] (C:\Users\Jakob\Documents\Bots\API\PiMusicPlayerV2\node_modules\express\lib\router\layer.js:95:5)
    at C:\Users\Jakob\Documents\Bots\API\PiMusicPlayerV2\node_modules\express\lib\router\index.js:284:15
    at Function.process_params (C:\Users\Jakob\Documents\Bots\API\PiMusicPlayerV2\node_modules\express\lib\router\index.js:346:12)
    at next (C:\Users\Jakob\Documents\Bots\API\PiMusicPlayerV2\node_modules\express\lib\router\index.js:280:10)
    at urlencodedParser (C:\Users\Jakob\Documents\Bots\API\PiMusicPlayerV2\node_modules\body-parser\lib\types\urlencoded.js:91:7)
    at Layer.handle [as handle_request] (C:\Users\Jakob\Documents\Bots\API\PiMusicPlayerV2\node_modules\express\lib\router\layer.js:95:5)

我可以毫无问题地写入数据库，但是当我尝试从中读取时出现上述错误，我该怎么办？

Answer 1

我认为您正在覆盖播放列表变量。 该文件是播放列表，当您获得元素时，您也将其分配给播放列表

此外，文件不是数据库

Answer 2

app.get("/playlist", (req, res) => {
console.log(playlist.get("playlist"))
let playlist = playlist.get("playlist")

第二行console.log(playlist.get("playlist"))正在尝试打印播放列表变量，但它在下一行中声明，因此无法访问该特定变量，因此错误。 您只能在初始化后访问某些内容。