Concatenating strings on Google Earth Engine

Question

I'm using the Javascript console on Google Earth Engine, and I'm stumped by a simple problem. I want to concatenate and print two values on one line. One of them is an object property.

When I use a comma to separate the parts in the print statement, I get the output I want, except that it is printed on separate lines. When I use a plus ('+'), the object's toString method is invoked and I get vastly more output than I want.

var img = ee.Image(img_list.get(0)) //grab an image
var date_index = img.get('system:index'); //get its date index property

print('MOD13Q_', date_index);
//Output (basically what I want, except on two lines instead of one)
//'MOD13Q_'
//'2018-01-17' 


print('MOD13Q_' + date_index); //Oops, '+' invoked the toString method
//'MOD13Q_ComputedObject({
  "type": "Invocation",
  "arguments": {
    "object": {
      "type": "Invocation",
      "arguments": {
        "list": {
          "type"....etc.

Is there any way to override the toString method, or to prevent it from being invoked? This question describes something similar, but does not show how to solve my problem.

Answer 1

Use server-side string method cat instead of JavaScript concatenation operator +.

var outStr = ee.String('MOD13Q_').cat(date_index);
print(outStr);

// OUT: 'MOD13Q_2018-01-17'