How Can I Streamline Nested Promises in NodeJS for Network Requests?

Removing Nested Promises

When working with network requests and promises using NodeJS, it is possible to encounter nested promises. While this is not inherently wrong, one may need to chain these promises together for a more streamlined flow.

The provided code snippet demonstrates a scenario where multiple nested promises are used to make API calls:

exports.viewFile = function(req, res) {
    var fileId = req.params.id;
    boxContentRequest('files/' + fileId + '/content', req.user.box.accessToken)
        .then(function(response) {
            boxViewerRequest('documents', {url: response.request.href}, 'POST')
                .then(function(response) {
                    boxViewerRequest('sessions', {document_id: response.body.id}, 'POST')
                        .then(function(response) {
                            console.log(response);
                        });
                });
        });
};

To chain these promises, a simple modification is required:

exports.viewFile = function(req, res) {
    var fileId = req.params.id;
    boxContentRequest('files/' + fileId + '/content', req.user.box.accessToken)
      .then(function(response) {
          return boxViewerRequest('documents', {url: response.request.href}, 'POST');
      })
      .then(function(response) {
          return boxViewerRequest('sessions', {document_id: response.body.id}, 'POST');
      })
      .then(function(response) {
          console.log(response);
      });
};

The key to this approach is to return the new promise from each then callback:

.then(function(response) {
    return nextPromise;
})

This ensures that the promise chain continues and resolves with the value from the "inner" promise. By chaining these promises, you can create a more readable and maintainable codebase.

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