I've tested this on the frontend of the imask (https://imask.js.org/) website, and can confirm that when you use a forward slash for the date formatting it refuses to allow the final digit of the date.
I have tried using:
IMask(
field,
{
mask: Date,
pattern: 'd{\/]}`m{\/}`Y',
min: new Date(1990, 0, 1),
max: new Date(2020, 0, 1),
lazy: false
});
IMask(
field,
{
mask: Date,
pattern: 'd{/]}`m{/}`Y',
min: new Date(1990, 0, 1),
max: new Date(2020, 0, 1),
lazy: false
});
IMask(
field,
{
mask: Date,
pattern: 'd/m/Y',
min: new Date(1990, 0, 1),
max: new Date(2020, 0, 1),
lazy: false
});
Anything but forward slashes works.