Gee calculated area

1. Calculation area of vector data (main function)

var stateArea = somewhere.geometry().area()
var stateAreaSqKm = ee.Number(stateArea).divide(1e6).round()
print(stateAreaSqKm)

2. Grid image calculation area (main function)
Ideas ：1） In pixels , Calculate the area of each pixel in the region of interest ;2） Perform summary summation , Calculate the area of the whole area ;3） Converting units .

//ee.Image.pixelArea():
//Generate an image in which the value of each pixel is the area of that pixel in square meters.
//The returned image has a single band called "area."
var area_image = image.eq(1).multiply.(ee.Image.pixelArea())

var area= area_image.reduceRegion({
    
    reducer:ee.Reducer.sum(),//calculate sum values within the aoi.
    geometry:aoi,//shp.geometry()
    crs:'EPSG:32749',
    scale:20,
    maxPixels:lel3,
})

//convert sqkm
var area_sqkm = ee.Number(
  area.get(0)).divide(1e6).round()//round():computes the integer nearest to the input

print(area_sqkm )

ee.Image.reduceRegion:

Reference material ：
See official documents when encountering functions you don't understand ：https://developers.google.com/earth-engine/apidocs

Calculating Area in Google Earth Engine：https://spatialthoughts.com/2020/06/19/calculating-area-gee/

Google Earth Engine (GEE) and Image Analysis