cannot set header before they are sent to client error

Question

I am facing error while showing JSON response.

My code is here.

app.get('/api/:id/:uid?',(req,res)=>{//? mean optional parameter
    console.log(req.params);// to get parameter in console
    const id=req.params.id*1;
    console.log(id);
    const tour=tours.find(el=>el.id===id);
    res.status(200).json({
        "staus":"success",
        "tours":tour
    })
    res.send("done");
})

showing Cannot set headers after they are sent to the client

Answer 1

I think error message is Cannot set headers after they are sent to the client, not before. It means that you already sent response back to the client. Just remove res.send("done"); this line.

But, be careful about other case like below. You'll also get Cannot set headers after they are sent to the client.

app.get("/path", (req, res) => {
    some_condition = true
    if (some_condition) {
        res.status(200).json({success: true})
    }
    res.status(200).json({success: false})
})

So, you should add return in front of res.status(200).json({success: true}) like below.

app.get("/path", (req, res) => {
    some_condition = true
    if (some_condition) {
        return res.status(200).json({success: true})
    }
    res.status(200).json({success: false})
})

Then, it'll not show up Cannot set headers after they are sent to the client this error message.