I am studying because I want to publish my results through Google Earth Engine. Regarding the usage of if / else and ee.Algorithms.If(), I don't understand why both true case and false case work.

As per Code, I want to check if the value selected from ui.Select scorresponds to List v.

var s = ui.Select({
  items: [
      {label: 'A', value: 'A'},
      {label: 'B', value: 'B'},

var b = ui.Button('Go!');

//var v = ee.List(['A', 'B', 'C']);
var v = ee.List(['C']);

function b_function(){
  ee.Algorithms.If(v.contains(s.getValue()), print('True!'), ui.root.add(ui.Label({value:'False!'})));



Is this possible even with a general if / else statement in google earth engine?

function b_function(){

1 Answer 1


The issue here is a mix up between client- and server-side. I would suggest that you read up on it here.

Your condition is server-side, so you cannot use a regular if statement. On the other hand, your actual actions are both client-side.

All arguments of ee.Algorithms.If() will be evaluated immediately, and both are performing client-side operations before the condition has even been evaluated. The common use of ee.Algorithms.If() is to use the return value, which will be different based on the condition. This server-side return value, ee.String in the example below, can then be turned into a client-side value using evaluate():

  ).evaluate(function (value) {
    ui.root.add(ui.Label({value: value}))

But you can just as well turn your condition into a client side object and use client-side conditional logic:

  v.contains(s.getValue()).evaluate(function (contains) {
    if (contains) {
    } else {
      ui.root.add(ui.Label({value: 'False!'}))


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