Return the number of days between two dates

// Write a function that takes two date instances as argument
// It should return the number of days that lies between those dates
function
myFunction
(
a, b
)
{

return
}
Test Cases:
myFunction(new Date('2020-06-11'), new Date('2020-06-01'))
Expected
10
myFunction(new Date('2000-01-01'), new Date('2020-06-01'))
Expected
7457