NodeJS , how to send response during Promise .then? - node.js

Question

I have the following code:
User.getConfByID(userID)
.then((item)=>{
if(item.length == 0){
res.status(400).json({error:"NO_USER_FOUND"})
}else{
if(item[0].token == token){
if((Math.abs(Date.now() - item[0].conf_iat)) > tokenValid){
res.status(401).json({error: "TOKEN_INVALID"})
}else{
return mariaDBTemplates.updateOneRowTemplate("User_confirmation", {confirmed:1}, "user_id", userID)
}
}else{
res.status(401).json({error: "TOKEN_NOT_SAME"})
}
}
})
.then(()=>{
res.status(200).json({success: "CONFIRMED"})
})
.catch((err)=>{
res.status(500).json({error: err.message})
})
You see I have different kinds of error messages with different kinds of status codes. When I run this code, it always gives me this warning:
Error: Can't set headers after they are sent
I think this is because i don't "break" the Promise after sending a response right?. But how can I solve this? Any suggestions?
Cheerio

Answer 1

your problem is with your promise chain. in your first .then, you always set the response with res, but the next .then in the chain tries to set the response again. Note that not returning anything from a promise is the same as return Promise.resolve(undefined);.
here's how I would do it:
User.getConfByID(userID)
.then((item) => {
if(item.length == 0)
return { statusCode: 400, body: { error: "NO_USER_FOUND" } };
else {
if(item[0].token == token) {
if((Math.abs(Date.now() - item[0].conf_iat)) > tokenValid)
return { statusCode: 401, body: { error: "TOKEN_INVALID" } };
else {
//not sure what this returns, but it looks like this is
//what you're trying to return the 200 for
mariaDBTemplates.updateOneRowTemplate("User_confirmation", { confirmed: 1 }, "user_id", userID);
return { statusCode: 200, body: { success: "CONFIRMED" } };
}
} else
return { statusCode: 401, body: { error: "TOKEN_NOT_SAME" } };
}
})
.then((result) => {
res.status(result.statusCode).json(result.body);
})
.catch((err) => {
res.status(500).json({ error: err.message });
});
Also note that returning a value from a promise is the same as returning Promise.resolve(value);, and will continue the promise chain.