errors.js

// inside computed
formErrors() {
    return {
    firstNameError: () => {
       if(!this.editCustomer.firstName){
        return this.errorMessages.blankError
      }
    },
      lastNameError: () => {
        if(!this.editCustomer.lastName){
        return this.errorMessages.blankError
      }
    },
      emailError:() => {
        !this.editCustomer.email){
        return this.errorMessages.blankError
      }
    }
  },
  
  
   <fg-input
    v-model="editCustomer.firstName"
    placeholder="First Name"
    label="First Name"
    name="firstName"
    ///called here
    :error="formErrors.firstNameError()"
  ></fg-input>