Google Apps Script Redeclaration of Const Error

Question

Given this Google Apps Script script:

'use strict'
const foo = 2;
function bar() {
  Logger.log(foo + 2);
}

Running the function bar results in a TypeError: redeclaration of const foo.

Why? How is foo being redeclared?

Answer 1

Seems like it's due to spotty implementation of ES6. I still get the error if I remove foo from the function, so the error is coming from the global const declaration. The below code produces the same error, but no error if you comment out const foo.

const foo = 2;

function bar() {
  const bar = 2;
  Logger.log(bar + 2);
}

See Google Apps Script Javascript Standard Support, in particular the first comment.

Answer 2

From Apps Script const scoping problems

Avoid using const in Apps Script for now. It just doesn't work as it should. For now it's just a half baked version of var.

From the same source

Apps Script is based on ES3 JavaScript, with quite a few additions from ES5 and even ES6.

To read the primary source go to https://developers.google.com/apps-script/guides/services/#basic_javascript_features