How to run a section of a script in the background

I know how to run a system process in the background, using shell script or AppleScript.

sf.system.exec({
            commandLine: `
            Shell script goes here
            `,
            executionMode: 'Background',
        });

And I also know how to combine separate background processes:

sf.system.exec({
            commandLine: `
            Process 1 &
            Process 2 &
            wait
            `,
            executionMode: 'Background',
        });

However in my example below I want to run a larger portion of a script, including Javascript, as a background process, but the result of each separate process is a variable so I'm not sure if I can combine them. The processes take quite long to run sometimes and I want to continue working while I wait, and also have access to my other Soundflow commands.

// I want to start background process here

let folderSizeCheckCurrentDropbox = sf.system.exec({
    commandLine: `
            rclone size --json "${rcloneFolderDropbox}"
            `,
    executionMode: 'Background',
}).result;

const objDropbox = JSON.parse(folderSizeCheckCurrentDropbox);
let folderSizeCheckCurrentDropboxValue = objDropbox.bytes;

let folderSizeCheckCurrentGoogleDrive = sf.system.exec({
    commandLine: `
            rclone size --json "${rcloneFolderGoogleDrive}"
            `,
    executionMode: 'Background',
}).result;

const objGoogleDrive = JSON.parse(folderSizeCheckCurrentGoogleDrive);
let folderSizeCheckCurrentGoogleDriveValue = objGoogleDrive.bytes;

// This is the end of the section that should run in the background

Is there a way of putting normal Javascript or Soundflow code inside a background process?