Converting a JSON object to a Float in Google Earth Engine

Question

I'm using Google Earth Engine for a GIS project and I'm extracting an average density from a WorldPop layer and for a precise area defined by a geometry. Further in my code, I want to use this average density as a float, here is my code :

// Layer used for population density
var datapop = ee.ImageCollection("WorldPop/GP/100m/pop").mosaic().clip(geometry_pop) ;

// Average, max and minimum population density for the selected area
var density = datapop.reduce(ee.Reducer.first()).reduceRegion(ee.Reducer.mean(),geometry_pop,100).get('first');

I've tried some prints to see what was the type conversion problem :

print(typeof density)                 //prints JSON object
print(typeof parseFloat(density))     //prints JSON number

var test = 9.0 ;
print(typeof test)                    //prints JSON number

print(density)                //prints 9.960041574584405
print(parseFloat(density))    //prints NaN

Does someone know how can I convert my JSON object into a JSON number without getting its value to NaN ?

Answer 1

Everything Earth Engine does is server-side; all of the variables you have in your browser are just proxy objects describing what computation to perform. In order to get a computed value into the browser, you have request the result using either getInfo() (print does this for you automatically) or evaluate().

See this page for more information: https://developers.google.com/earth-engine/guides/client_server

That said, if you're going to continue to use the result in Earth Engine, you don't need to do that, you just pass the object into the next function.