JS scope/closure issue

Question

The code below prints out Value: undefined because (I assume) the scope of the console.log() statement is ExternalLibrary where there is no x defined. So how so I resolve the issue? I'm guessing there is a solution using closures but cannot figure out what it is.

class ExternalLibrary {
    callback
    setup(callback) {
        this.callback = callback
    }
    call() { this.callback() }
}

class Main {
    x = 1

    doIt() {
        const lib = new ExternalLibrary()
        lib.setup(function () {
            console.log('Value: ' + this.x)
        })
        lib.call()
    }
}

new Main().doIt()