类型错误：回调不是 nodejs 中的函数
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TypeError: callback is not a function in nodejs
提问by
I am trying learn nodejs and stumble upon this error
我正在尝试学习 nodejs 并偶然发现此错误
TypeError: callback is not a function
类型错误：回调不是函数
when I am trying to call the server using this command.
当我尝试使用此命令调用服务器时。
curl http://localhost:8090/albums.json
curl http://localhost:8090/albums.json
and here is the code for my server.js
这是我的 server.js 的代码
var http = require('http'),
fs = require('fs');
function load_album(album_name, callback) {
fs.readdir("albums/", +album_name, (err, files) => {
if (err) {
if (err.code == "ENOENT") {
callback(make_error("no_such_album", "That album doesn't exist"));
} else {
callback(make_error("can't load album", "The server is broken"));
}
} else {
//callback(null, files);
var only_files = [];
var path = 'albums/${album_name}/';
var iterator = (index) => {
if (index == files.length) {
var obj = {
short_name: album_name,
photos: only_files
};
callback(null, obj);
return;
}
fs.stat(path + files[index], (err, stats) => {
if (!err && stats.isFile()) {
only_files.push(files[index]);
}
iterator(index + 1);
});
};
iterator(0);
}
});
}
function handle_incoming_request(req, res) {
console.log("incoming request: " + req.method + " " + req.url);
if (req.url == '/albums.json') {
load_album((err, albums) => {
if (err) {
res.writeHead(500, {
"Content-Type": "application/json "
});
res.end(JSON.stringify({
code: "cant_load_albums",
message: err.message
}));
} else {
var output = {
error: null,
data: {
albums: albums
}
};
res.writeHead(200, {
"Content-Type": "application/json"
});
res.end(JSON.stringify(output) + "\n");
}
});
} else if (req.url.substr(0, 7) == '/albums' && req.url.substr(req.url.length - 5) == '.json') {
//user is requesting contents of album
load_album(req.url.substr(7, req.url.length - 12), (err, photos) => {
if (err) {
res.writeHead(500, {
"Content-type": "application/json"
});
res.end(JSON.stringify(err));
} else {
var output = {
error: null,
data: {
photos: photos
}
};
res.writeHead(200, {
"Content-Type": application / json
});
res.end(JSON.stringify(output) + "\n");
}
});
} else {
res.writeHead(404, {
"Content-type": "application/json"
});
res.end(JSON.stringify({
code: "no_such_page",
message: "No such page"
}));
}
}
var s = http.createServer(handle_incoming_request);
s.listen(8090);can you tell me what's wrong with my code that I got an error telling me callback isn't a function?
你能告诉我我的代码有什么问题，我有一个错误告诉我回调不是一个函数吗？
thanks though
不过谢谢
for more formatted code then you can go here https://jsfiddle.net/02dbx6m9/
更多格式化代码，那么你可以去这里https://jsfiddle.net/02dbx6m9/
采纳答案by Vikas
var http = require('http'),
fs = require('fs');
function load_album(album_name, callback) {
fs.readdir("albums/", +album_name, (err, files) => {
if (err) {
if (err.code == "ENOENT") {
callback(make_error("no_such_album", "That album doesn't exist"));
} else {
callback(make_error("can't load album", "The server is broken"));
}
} else {
//callback(null, files);
var only_files = [];
var path = 'albums/${album_name}/';
var iterator = (index) => {
if (index == files.length) {
var obj = {
short_name: album_name,
photos: only_files
};
callback(null, obj);
return;
}
fs.stat(path + files[index], (err, stats) => {
if (!err && stats.isFile()) {
only_files.push(files[index]);
}
iterator(index + 1);
});
};
iterator(0);
}
});
}
function handle_incoming_request(req, res) {
console.log("incoming request: " + req.method + " " + req.url);
if (req.url == '/albums.json') {
load_album("ALBUM NAME", (err, albums) => {
if (err) {
res.writeHead(500, {
"Content-Type": "application/json "
});
res.end(JSON.stringify({
code: "cant_load_albums",
message: err.message
}));
} else {
var output = {
error: null,
data: {
albums: albums
}
};
res.writeHead(200, {
"Content-Type": "application/json"
});
res.end(JSON.stringify(output) + "\n");
}
});
} else if (req.url.substr(0, 7) == '/albums' && req.url.substr(req.url.length - 5) == '.json') {
//user is requesting contents of album
load_album("Album Name", req.url.substr(7, req.url.length - 12), (err, photos) => {
if (err) {
res.writeHead(500, {
"Content-type": "application/json"
});
res.end(JSON.stringify(err));
} else {
var output = {
error: null,
data: {
photos: photos
}
};
res.writeHead(200, {
"Content-Type": application / json
});
res.end(JSON.stringify(output) + "\n");
}
});
} else {
res.writeHead(404, {
"Content-type": "application/json"
});
res.end(JSON.stringify({
code: "no_such_page",
message: "No such page"
}));
}
}
var s = http.createServer(handle_incoming_request);
s.listen(8090);You forgot to pass album name parameter in load_album method. That's why album_name parameter is assigned the actual callback, while callback parameter remains undefined.
您忘记在 load_album 方法中传递专辑名称参数。这就是为什么为专辑名称参数分配了实际回调，而回调参数保持未定义的原因。
回答by Filip Dupanovi?
Here is the root cause of your issue:
这是您问题的根本原因：
load_album((err, albums) => {
// ...
});
The signature for the function requires two parameters, yet you're only passing the first one:
该函数的签名需要两个参数，但您只传递第一个参数：
function load_album(album_name, callback) {}
Therein, once called, callbackwill be undefined, yet you're trying to treat it as a callable. Here's a more succint example of how to reproduce the error:
其中，一旦被调用，callback将是未定义的，但您试图将其视为可调用的。下面是如何重现错误的更简洁的示例：
function foo(bar, baz) {
baz()
}
foo(() => {})