ERR_HTTP_HEADERS_SENT: Cannot set headers after they are sent to the client at ServerResponse

Question

I am trying to create a simple REST API with NodeJS and Express without any database. I have stored all of my data in JSON files. The data is in the form of an array of objects.

I have paths like fund-name/:portId

so I am doing this:

const fundName = require('./json/fund-name.json');

app.get('/fund-details:portId', (req, res) => {

    const portId = req.params.portId;
    fundDetails.forEach(fund => {
        if (fund.portId === portId) {
            return res.json(fund);
        }

        return res.json([]);
    });
});

when I hit the url http:localhost:3000/fund-details/1234, I get the following error:

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client at ServerResponse.setHeader (_http_outgoing.js:470:11) at ServerResponse.header (/home/username/Desktop/data-server/node_modules/express/l ib/response.js:767:10)

It works fine when I don't pass any path param to get all the funds. Where am I going wrong??

Answer 1

This error is because you are using res.send() multiple time in single api call.
Correct way

if(a){
 res.send()
}else{
 res.send()
}

Wrong way

if(a){
 res.send()
 res.send()
}else{
 res.send()
}

In your code.

app.get('/fund-details:portId', (req, res) => {
const portId = req.params.portId;
fundDetails.forEach(fund => {
    if (fund.portId === portId) {
        return res.json(fund); // many or single times here
    }
    return res.json([]); // and here when fund !==portId here 
});
});

You can try

app.get('/fund-details:portId', (req, res) => {

const portId = req.params.portId;
var flag 
var data = []
fundDetails.forEach(fund => {

 if (fund.portId === portId) {
       flag=true
       data.push(fund)
    }
});
if(flag){
    res.send(data);
}else{
    res.send()
}
});