Keep track of how many times a recursive function was called

Answer 1

Why not make a call to console.count in your function ?

Edit: Snippet to try in your browser :

function singleDigit(num) {
    console.count("singleDigit");

    let counter = 0
    let number = [...num + ''].map(Number).reduce((x, y) => {return x * y})

    if(number <= 9){
        console.log(number)
    }else{
        console.log(number)
        return singleDigit(number), counter += 1
    }
}
singleDigit(39)

I have it working in Chrome 79 and Firefox 72