Array.sort() on multiple properties

I have an array, productData with multiple properties. This is how I currently sort the array by monthlyCost, ascending.
How can I modify this to sort all items by a boolean property isPromoted, followed by monthlyCost?
My array should start with all items where isPromoted == true sorted by monthlyCost, then all items where isPromoted == false sorted by monthlyCost.

    productData.sort((a, b) => {
      if (a.monthlyCost > b.monthlyCost) {
        return 1;
      } else if (a.monthlyCost < b.monthlyCost) {
        return -1;
      } else {
        return 0;
      }
    });

Answer

You can use this callback:

productData.sort((a, b) => +b.isPromoted - +a.isPromoted || a.monthlyCost - b.monthlyCost);

The unary plus is optional in plain JavaScript, but in a TypeScript context, you’ll need to be explicit about the conversion to number and apply +.