const rand = Math.random() * 1000;

const values = {
    firstName: 'M',
    lastName: 'J',
    company: 'pl',
    phone: '9999181910',
    companyPhone: '9999181910',
    panNo: 'adps9393l',
    password: 'hooping2',
    numberOfTrucks: '9',
    city: 'Kanpur',
    email: 'someone' + rand + '@s.com',
    userName: 'some' + rand
};

const f = document.forms[0];

f["trucker[user_attributes][first_name]"].value = values.firstName;
f["trucker[user_attributes][last_name]"].value  = values.lastName;
f["trucker[user_attributes][email]"].value = values.email;
f["trucker[user_attributes][primary_phone_no]"].value = values.phone;
f["trucker[user_attributes][password]"].value = values.password;
f["trucker[user_attributes][password_confirmation"].value = values.password;
f["trucker[company_name]"].value = values.company;
f["trucker[user_attributes][username]"].value= values.userName;
f["trucker[fleet_size]"].value = values.numberOfTrucks;
f["trucker[office_phone_no]"].value = values.companyPhone;
f["trucker[pan_no]"].value = values.panNo;
f["trucker[city]"].value = values.city;