ExampleComponent.js:

import ExampleValidator from '../validators/exampleValidator.js';
import User from '../models/user.js';

console.log("a");

let engin = new User(1, "Engin", "Demiroğ", "Ankara", 36)

let exampleValidator = new ExampleValidator();
// exampleValidator.checkValidity(engin);

EmployeeValidators.js:

import * as Yup from '../../node_modules/yup/lib/index.js';

export default class EmployeeValidators {
    constructor(){
        const validationSchema = Yup.object().shape({
            id: Yup.number().required('Id is required'),
            firstName: Yup.string().required('First name is required'),
            lastName: Yup.string().required('Last name is required'),
            age: yup.number().required().positive().integer(),
            city: Yup.string().required('City is required')
        });
    }

    // checkValidity(employee) {
    //     return validationSchema.isValid(employee);
    // }
}

Browser output image

Browser output text: Uncaught (in promise) ReferenceError: Error evaluating http://localhost:3000/src/validators/exampleValidator.js Error evaluating http://localhost:3000/node_modules/yup/lib/index.js exports is not defined at execute (index.js:7) at B (es6-module-loader-dev.src.js:1177) at E (es6-module-loader-dev.src.js:1238) at E (es6-module-loader-dev.src.js:1222) at E (es6-module-loader-dev.src.js:1222) at D (es6-module-loader-dev.src.js:1201) at C (es6-module-loader-dev.src.js:1194) at es6-module-loader-dev.src.js:855