添加拒绝/解决以捕获/成功

Question

I use the following code and I wonder for best practise usage if I should add reject to this promise inside the catch?

run: function (req, res) {

        if (req) {
            return this._un(req).then(function() {  
                return proce.restart().then(function() {                    
                    return res.status(200).end("sucess");   
                    //Here should I use reslove
                });                                                             
            }).catch(function(err) {                
                return res.status(500).send("error: " + err);
                //Here should I use reject???               
            });                     
        }
        else {          
            return new Promise(function(resolve, reject) {  
                reject("No application content found");
            });         
        }       
    }
};

Answer 1

You don't "add reject" to a promise. A promise is either unsettled, or settled (resolved/rejected).

If req is provided, your code currently returns a promise that will be resolved with the return value of end (if the restart was successful) or the return value of send (if it wasn't), which I believe in both cases is the response object itself ( res ).

If you want the caller to be aware of whether the restart was successful, then yes, you want to reject the promise instead; with ES2015 promises you can do that by throwing in catch and I assume Bluebird is similar:

.catch(function(err) {
    res.status(500).send("error: " + err);
    throw err; // Or `throw new Error(err);`, it depends on what `err` is and your convention
})

...or by using Bluebird's Promise.reject (which is also ES2015-compatible):

.catch(function(err) {
    res.status(500).send("error: " + err);
    return Promise.reject(err);
})

If you don't want the caller to be aware of whether the restart was successful, then don't.