specifications.js

const emailSpecification = email => {
  
  const expression = 'user.email === email';
    
  return {
    isSatisfiedBy(user) {
      return eval(expression);
    } 
  };

};



const u = {
  email: 'email@gmail.com',
  isActive: false,
};


const isActiveSpecification = {
  isSatisfiedBy(user) {
    return !!user.isActive;
  }
};

const compose = (...specs) => {
  const specifications = specs.length === 1 ? specs[0] : specs;
  
  return {
    specifications,
    operator: 'AND',
    isSatisfiedBy(obj) {
      for (let i = 0; i < specifications.length ; i++) {
        if (!specifications[i].isSatisfiedBy(obj)) return false;
      }
      return true;
    }
  }
}

const not = (spec) =>({
  spec,
  operatior: 'NOT',
  isSatisfiedBy(obj) {
    return !spec.isSatisfiedBy(obj);
  }
});

const and = compose;

const or = (...specs) => {
  const specifications = specs.length === 1 ? specs[0] : specs;
  
  return {
    specifications,
    operator: 'OR',
    isSatisfiedBy(obj) {
      for (let i = 0; i < specifications.length ; i++) {
        if (specifications[i].isSatisfiedBy(obj)) return true;
      }
      return false;
    }
  }
}


const finalSpec = compose(
  emailSpecification('email@gmail.com'), 
  not(isActiveSpecification)
);

const finalSpec2 = compose([emailSpecification('email@gmail.com'), isActiveSpecification]);

const finalSpec3 = or(emailSpecification('alex.a'), isActiveSpecification)


const res = emailSpecification('email@gmail.com').isSatisfiedBy(u);
const res1 = finalSpec.isSatisfiedBy(u);
const res2 = finalSpec2.isSatisfiedBy(u);
const res3 = finalSpec3.isSatisfiedBy(u);

console.log(res);
console.log(res1);
console.log(res2);
console.log(res3);