node.js无法使用res.json设置标头错误

Question

if (user) {

    if (userId != user._id) {
        res.json({success: false, msg: 'Invalid request, wrong secret key'});
    }

    User.comparePassword(password, user.password, function (err, result) {
        if (result === true) {

            res.json({success: true, msg: 'ok'});
        } else {
            res.json({success: false, msg: 'Error, Incorrect password!'});
        }
    });
} else {
    res.json({ success: false, msg: 'Error, account not exist!'});
}

I thought the first res.json will stop the following res.json but in this case I seem can't use the first res.json, I don't know why.

Answer 1

res.json() sends the response, but it does not prevent the rest of your code from running.

As such, you have some code paths that attempt to send res.json() twice which will cause the error message you are seeing. You need to prevent that either with appropriate if/then blocks or by inserting appropriate return statements.

I'd suggest this:

if (user) {

    if (userId != user._id) {
        res.json({success: false, msg: 'Invalid request, wrong secret key'});
        return;
    }

    User.comparePassword(password, user.password, function (err, result) {
        if (result === true) {

            res.json({success: true, msg: 'ok'});
        } else {
            res.json({success: false, msg: 'Error, Incorrect password!'});
        }
    });
} else {
    res.json({ success: false, msg: 'Error, account not exist!'});
}

But, you also could fix it by adding an else to the first if and putting the rest of the code inside that.