Question

每次其他时，我都会通过对most_voted的ajax调用加载页面，但是出现以下错误。为什么会这样？

错误

http.js:692
throw new Error('Can\'t set headers after they are sent.');
^
Error: Can't set headers after they are sent.

控制器

// Add Voted Attribute
add_voted_attribute = function(user, product, callback) {
    Vote.find({ product: product._id, user: user._id }).exec(function(err, vote) {
        if (vote.length) {
            product       = product.toObject();
            product.voted = true;
            if (callback) { callback(product) };
        } else {
            product       = product.toObject();
            product.voted = false;
            if (callback) { callback(product) };
        };
    });
};


// Show Most Voted Products
exports.most_voted = function(req, res) {
        Product.find().sort({votes: -1}).limit(10).populate('user', 'name username').exec(function(err, products) {
            var products_with_voted_attribute = [];
            products.forEach(function(p){
                add_voted_attribute(req.user, p, function(product){
                    products_with_voted_attribute.push(product);
                    if (products_with_voted_attribute.length === 10) { 
                        eventEmitter.emit('mostVoted', products_with_voted_attribute); 
                    };
                });
            });
        });
        // Event Listener
        eventEmitter.on('mostVoted', function(products)  {
            products.sort(function(obj1, obj2) {
                return obj2.votes - obj1.votes;
            });
            res.jsonp(products);
        });
};

Answer 1

每个请求只能调用一次res.jsonp。多次调用会导致多次发送标题（内容类型）。

Answer 2

eventEmitter多次触发。我不确定为什么会这样，但我通过在触发一次之后删除事件监听器来解决它。此修复只需要一行代码：

// Event Listener
        eventEmitter.on('mostVoted', function(products)  {
            eventEmitter.removeAllListeners('mostVoted'); // Line of code to remove listener

为什么我在节点中收到此错误：错误：发送后无法设置标头

2 个答案: