Accuracy assessment resulting values as strings in GEE

Question

I am trying to create a panel that shows a value on the map. The value should show the resulting value of an accuracy assessment(for instance: ConfusionMatrix.accuracy()). I am using the following piece of code:

var acc_val= ee.String(trainAccuracy.accuracy())

var legendTitle = ui.Label({
  value: 'Overall Accuracy:'+  acc_val , 
  style: {
    fontSize: '18px',
    margin: '0 0 4px 0',
    padding: '0'
    }
});
Map.add(panel);
panel.add(legendTitle);

where acc_val should be a number or string, but it shows a long list of characters.

This is what I get:

This is what I expect:

The code is here.

Answer 1

You get this because you do client-side concatenation on acc_val, which is a server-side object. Read Client vs. Server in the Earth Engine docs for an explanation. You can convert acc_val to a client-side object with evaluate():

var acc_val = ee.String(trainAccuracy.accuracy()) // Server-side object

acc_val.evaluate(function(value) { // Turn acc_val into client-side object
  var legendTitle = ui.Label({
    value: 'Overall Accuracy: ' + value,
    style: {
      fontSize: '18px',
      margin: '0 0 4px 0',
      padding: '0'
    }
  });
  Map.add(panel);
  panel.add(legendTitle);
})