Calculate the number of months between two dates

const monthDiff = (startDate, endDate) =>
    Math.max(0, (endDate.getFullYear() - startDate.getFullYear()) * 12 - startDate.getMonth() + endDate.getMonth());

const monthDiff = (startDate: Date, endDate: Date): number =>
    Math.max(0, (endDate.getFullYear() - startDate.getFullYear()) * 12 - startDate.getMonth() + endDate.getMonth());

monthDiff(new Date('2020-01-01'), new Date('2021-01-01')); // 12