Summary Statistics of Points with User Defined Polygon

Hello,

What I am trying to do is build a web app with the JavaScript API that will show tree inventory point data of a city and allow the user to draw a polygon to select trees and return back a sum of CO2 sequester amounts (the numbers I have in one column of the data) for the selected points in the polygon.

I have tried using model builder to replicate this and got it to work in ArcMap with the Summary Statistics tool but when I navigated back to the tool after closing ArcMap my polygon would no longer complete and all the model returned was the sum of all the values for all the points in the layer.

I also tried using Select by Location and that will select the points, but I can't figure out how to get a summary of those points selected, and now since I've closed and opened that tool I have the same problem with the polygon not allowing the user to complete/finish it.

Can anyone tell me if this is the correct approach at all if my goal is to put the model on a server as a geoprocessing tool and use it with the JavaScript API? Is there a way to do this just in JavaScript by calling on the layer copied to the server?

I am new to JavaScript and somewhat new to ArcGIS in general.

Any help is appreciated.


Thanks.