Node + Promise + Phantom.JS - Strange Error

I am using Node and npm phantom to make screenshot of many webpages. To save CPU I use one Phantom instance per process. In this instance I am opening a page, render it, close it and go on.

This works really great except when I am starting another process. In this case I get this error, when one process is done:

UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 2): Error: undefined is not an object (evaluating 'target[command.params[0]]')

Phantom instance:

function initPhantom(todos) {
    phantom.create(['--ignore-ssl-errors=no'], {logLevel: 'error'})
        .then(function (instance) {
            var processId = instance.process.pid;
            console.log("===================> instance: ", processId);
            phInstance = instance;
            webshot(0, todos);
        });
}

Loop through URLs:

function webshot(id, shots) {
        phInstance.createPage().then(function (_page) {
                sitepage = _page;
                sitepage.property('viewportSize', {width: 1024, height: 768});
                WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.120 Safari/537.36');
                sitepage.setting("resourceTimeout", 4000);
                return sitepage.open(shots[id].url);
            })
            .then(function (status) {
                console.log("render %s / %s", id + 1, shots.length);
                setTimeout(function () {
                    var image = 'temp_img/' + shots[id]._id + '.png';
                    sitepage.render(image, {format: 'png', quality: '30'}).then(function (finished) {
                        sitepage.close();
                        chekcImageinDb(shots[id], image);
                        if (id < shots.length - 1) {
                            id += 1;
                            webshot(id, shots);
                        } else {
                            console.log("===================> all done: %s files has been written", shots.length);
                             phInstances.shift();
                            if(phInstances.length < 1){
                                 console.log("kill phantom ", phInstances);
                                //phInstance.exit();
                            }
                        }
                    });
                }, 2000);
            })
    }

Any idea

-------- edit -----------

OK I tried your suggestions, same error. As you can see in the log, it only occurs after one process is done.

function webshot(id, shots) {
        phInstance.createPage().then(function (_page, error) {
            if(error){
                console.log("first", error);
            }
                sitepage = _page;
                sitepage.property('viewportSize', {width: 1024, height: 768});
                WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.120 Safari/537.36');
                sitepage.setting("resourceTimeout", 4000);
                return sitepage.open(shots[id].url);
            }).catch(function(e) {
                console.log(e);
            }).then(function (status, error) {
                if(error){
                    console.log(error)
                }
                console.log("render %s / %s", id + 1, shots.length);
                setTimeout(function () {
                    var image = 'temp_img/' + shots[id]._id + '.png';
                    sitepage.render(image, {format: 'png', quality: '30'})
                        .then(function (finished, error) {
                        if(error){
                            console.log(error)
                        }
                        sitepage.close();
                        chekcImageinDb(shots[id], image);
                        if (id < shots.length - 1) {
                            id += 1;
                            webshot(id, shots);
                        } else {
                            console.log("===================> all done: %s files has been written", shots.length);
                             phInstances.shift();
                            if(phInstances.length < 1){
                                 console.log("kill phantom ", phInstances);
                                //phInstance.exit();
                            }
                        }
                    }).catch(function(e) {
                        console.log(e);
                    });
                }, 2000);
            }).catch(function(e) {
            console.log(e);
        })
    }

Here is the log file for two instances started nearly at the same time. Like I said, if just one process is running, everything works great.

Solution

I think you need to pass a 2nd callback function to your then function calls for the failure handlers. Depending on the interface, you may instead need to chain a .catch(function(){}) after your then() calls.