How to chain multiple paging request with node-apac?

Question

I'm new to Javascript and Nodejs and I am trying to setup a server which can request multiple ItemPages from amazon-product-api via the node-apac node package. So far my http server is up and running with some routes defined. I can also request a single ItemPage. But I have trouble chaining the requests.

example for theQuery:

var query = {
    Title: theTitle,
    SearchIndex: 'Books',
    BrowseNodeId: '698198',
    Power: 'binding:not (Kindle or Kalender)',
    Sort: '-publication_date',
    ResponseGroup: 'ItemAttributes,Images',
    ItemPage: 1
};

the code:

AmazonWrapper.prototype.getAllPagesForQuery = function(theMethod, theQuery, theResultCallback) {    
    client.execute(theMethod, theQuery).then(function(theResult) {
        var pageCount = theResult.result.ItemSearchResponse.Items.TotalPages;
        var requests = [];
        for(var i = 2; i < pageCount; i++) {
            theQuery.ItemPage = i;
            requests.push(client.execute(theMethod, theQuery));     
        }
        Promise.all(requests).then(function(theResults) {       
            var data = theResults[0];
            for(var i = 1; i < theResults.length; i++) {
                var items = theResults[i].result.ItemSearchResponse.Items.Item;
                data.result.ItemSearchResponse.Items.Item.concat(items);
            }
            theResultCallback(data);
        });
    });
};

As you see I want to read from the first request how many Itempages are available for my ItemSearch und create a new request for each Itempage. Unfortunately Promise.all(...).then() is never called.

Any help is appreciated

Answer 1

theQuery looks like an object. As such, it is passed by pointer to when you do theQuery.ItemPage = i and then you pass theQuery, you're passing the same object to every single request and just overwriting the ItemPage property on that one object. This is unlikely to work properly.

I don't know exactly what theQuery is, but you probably need to make copy of it.

Also, you may as well return a promise from .getAllPagesForQuery() rather than use a callback since you're already using promises. Error handling and chaining is a whole lot easier with promises all the way through.

You don't quite disclose enough code, but here's the general idea for how to fix:

AmazonWrapper.prototype.getAllPagesForQuery = function(theMethod, theQuery) {    
    return client.execute(theMethod, theQuery).then(function(theResult) {
        var pageCount = theResult.result.ItemSearchResponse.Items.TotalPages;
        var requests = [];
        for(var i = 2; i < pageCount; i++) {
            // make unique copy of theQuery object
            var newQuery = Object.assign({}, theQuery);
            newQuery.ItemPage = i;
            requests.push(client.execute(theMethod, newQuery));     
        }
        return Promise.all(requests).then(function(theResults) {       
            var data = theResults[0];
            for(var i = 1; i < theResults.length; i++) {
                var items = theResults[i].result.ItemSearchResponse.Items.Item;
                 data.result.ItemSearchResponse.Items.Item = data.result.ItemSearchResponse.Items.Item.concat(items);
            }
            return data;
        });
    });
};

// Usage example:
obj.getAllPagesForQuery(...).then(function(data) {
    // process returned data here
});