how to assert error thrown with expect(fn).to.throw(Error) in Cypress

[MinhTran1997]

Scenario:
i have a input field and a button, both have "disabled" class and cannot be typed in or clicked. i want to check if whether they can be typed in, clicked or not. things would be easy if i just check if there is a "disabled" class in their html attr. but i want to do in a different way, whenever i run Cypress code that make a type in action or a click action cy.get(input).type(....), error will be thrown when running test case. so i want to use expect(fn).to.throw(Error) assertion to catch that error

when i run cypress code, there will be 2 functions, one is to cy.get(input field).type('...') and one is to cy.get(button).click(). then i will check when these two functions being executed, expect the errors will be thrown after typing in or clicking, if true, the test case will pass.

Code is something like this:
cy.get(input[id='input']).should('be.visible').then(() => { function typeName () { cy.get(input[id='input']).type('some thing'); } expect(typeName).to.throw(Error); })

Current status:
test case fails, it seems like i the function typeName() doesn't run so there is no error to assert:
assert: expected [Function: typeName ] to be a function (PASS)
assert: expected [Function: typeName ] to throw Error (FAIL)

many thanks.

Minh