const login = () => { cy.get('#user').type('admin'); cy.get('#pass').type('1234'); cy.get('#submit').click(); } uses a valid arrow function assigned to a constant, which is common in Cypress helper files.
Step 2: Check other options for syntax errors
function login() { cy.get('#user').type('admin'); cy.get('#pass').type('1234'); cy.get('#submit').click(); } is a function declaration but not exported or assigned; cy.login = () => { cy.get('#user').type('admin'); cy.get('#pass').type('1234'); cy.get('#submit').click(); } incorrectly assigns to cy object; login() { cy.get('#user').type('admin'); cy.get('#pass').type('1234'); cy.get('#submit').click(); } is invalid syntax.