Creating two y-axis for time series pixel analysis using ui.Chart.image.series() in Google Earth Engine

Question

I am trying to create a time series image chart for GPP and LAI of a single pixel. The graph looks fine as far as the values are considered. I would like to add a title to both y-axis and have both y-axis have a minimum value of 0. I would post a picture of the graph that I currently have, but stack overflow will not let me.

Here is the script:

https://code.earthengine.google.com/18dedf6d2e871cfb9ce1869f15dd0d80

var chart = ui.Chart.image.series({
                                   imageCollection: modisVeg ,
                                   region: tree ,
                                   scale: 500   ,
                                   xProperty: 'system:index'
                                  })
                          .setSeriesNames(['GPP', 'LAI'])
                          .setOptions({
                            title: '[Time-series Analysis (2019)]: Tree Pixel' ,
                            series: {
                                     0: {
                                         targetAxisIndex: 0 ,
                                         type: "line" ,
                                         lineWidth: 5 ,
                                         pointSize: 0 ,
                                         color: "blue" 
                                        } ,
                                     1: {
                                         targetAxisIndex: 1 ,
                                         type: "line" ,
                                         lineWidth: 5 ,
                                         pointSize: 0 ,
                                         color: "green" 
                                        } ,
                                    } ,
                            hAxis: {
                                    title: 'Date' ,
                                    titleTextStyle: { italic: false, bold: true }
                                   } ,
                            vAxis: {
                                    0: {
                                        title: "GPP (g*C / m^2)" ,
                                        baseline: 0 ,
                                        titleTextStyle: { bold: true , color: 'blue' }
                                      } ,
                                    1: {
                                        title: "LAI" ,
                                        baseline: 0  ,
                                        titleTextStyle: { bold: true, color: 'green' }
                                      }
                                   } ,
                            curveType: 'function'
                          });

print(chart);

Answer 1

I answered this by changing one letter. Instead of vAxis, use vAxes! To set a minimum y-axis value for each one just add viewWindow: {min: 0} inside each y-axis.

var chart = ui.Chart.image.series({
                                   imageCollection: modisVeg ,                          // Image collection we want to use for timeseries analysis
                                   region: tree ,                                       // Pixel we want to use
                                   scale: 500   ,                                       // [Spatial Resolution]: 500
                                   xProperty: 'system:time_start'                       // Date 
                                  })
                          .setSeriesNames(['GPP', 'LAI'])
                          .setOptions({
                            title: '[Time-series Analysis (2019) ]: Tree Pixel' ,
                            series: {
                                     0: {
                                         targetAxisIndex: 0 ,
                                         type: "line" ,
                                         lineWidth: 5 ,
                                         pointSize: 0 ,
                                         color: "blue"
                                        } ,
                                     1: {
                                         targetAxisIndex: 1 ,
                                         type: "line" ,
                                         lineWidth: 5 ,
                                         pointSize: 0 ,
                                         color: "green" 
                                        } ,
                                    } ,
                            hAxis: {
                                    title: 'Date' ,
                                    format: "MM" ,
                                    titleTextStyle: { italic: false, bold: true }
                                   } ,
                            vAxes: {
                                    0: {
                                        title: "GPP (g*C / m^2 / day)" ,
                                        baseline: 0 ,
                                        titleTextStyle: { bold: true , color: 'blue' } ,
                                        viewWindow: { min: 0 }
                                      } ,
                                    1: {
                                        title: "LAI" ,
                                        baseline: 0  ,
                                        titleTextStyle: { bold: true, color: 'green' } ,
                                        viewWindow: { min: 0 }
                                      }
                                  } ,
                            curveType: 'function'
                          });

print("[Time-series for GPP (g*C / m^2 / day) and LAI]: " , chart);