How to keep and update a global variable in Google Apps Script

In a Google Apps Script, if you want to keep a value across many function executions, there's a service fo that: PropertiesService.

The PropertiesService allows to set key/value pairs that will be persistent over time.

There are three type of PropertiesService:

• document
• script
• user

The difference is in the permission the service allows according to the context.

Increment a counter

In my exploration, I want to have a counter that increments each time the function get called.

var scriptPrp = PropertiesService.getScriptProperties()
scriptPrp.setProperty('counter', 0)

function myFunc(){
  Logger.log('go!')
}

Now, run just one time the script in order to set the variable, it's like an init, then, modify the code this way:

var scriptPrp = PropertiesService.getScriptProperties()
// scriptPrp.setProperty('counter', 0)
// comment the above line otherwise it's be reset each time

function myFunc(){
  var counter = scriptPrp.getProperty('counter')
  counter++
  scriptPrp.setProperty('counter', counter)
}

As you can see, the counter variable is red and updated on each function call.

Let's use the counter to name folders

Suppose you want to create a Drive folder on each function run, giving a incremental name, here the script based on the previous exploration:

var scriptPrp = PropertiesService.getScriptProperties()

function myFunc(){
  
  var counter = scriptPrp.getProperty('counter')
  counter++
  scriptPrp.setProperty('counter', counter)
  
  var folderName = 'myFolder' + counter
  var newfolder = DriveApp.createFolder(folderName)
}

Now, on each run a folder il created named such as: myFolder1, myFolder2 and so forth.