An example of a functional-programming inspired validator

validator.js

import { of } from "rxjs/observable";
import { filter, map } from "rxjs/operators";
import validate, * as v from "libs/validate";

const validateForm = validate([
  v.field("name", "Full Name", [
    v.isRequired,
    "A full name is required.",
    name => name.split(" ").length,
    wordCount => wordCount < 2,
    "Please provide a first name and last name."
    wordCount => wordCount > 2,
    "Only a first name and last name is required."
  ]),
  v.field("email", "Email", [
    v.isRequired,
    "An email address is required",
    v.isEmail,
    "Please provide a valid email address.",
  ]),
  v.field("age", "Your Age", [
    v.isNumeric,
    "Age must be a numeric value",
    // naive, custom isInteger
    age => String(age) === String(parseInt(age, 10)),
    "Age must be a positive, whole number.",
    Number,
    age => age >= 62,
    "Sorry you are too young to collect social security.",
  ]),
  v.field("favorite_color", "Your Favorite Color", [
    v.isRequired,
    "A favorite color is required",
    color => color === "blue",
    "Sorry but your favorite color must be blue.",
  ]),
]);

const data = {
  name: "Amadaeus F. Blundershvlt",
  email: "amadaeus@example",
  age: 15,
};

of(data)
  .pipe(
    map(validateForm),
    // optional
    // filter(form => form.isValid === true)
  )
  .subscribe(console.log);

// =>
// {
//   data: {
//     name: "Amadaeus F. Blundershvlt",
//     email: "amadaeus@example",
//     age: 15,
//   }, 
//   isValid: false,
//   errors: [
//     {
//       name: "name",
//       label: "Full Name",
//       message: "Only a first name and last name is required.",
//     },
//     {
//       name: "email",
//       label: "Email",
//       message: "Please provide a valid email address.",
//     },
//     {
//       name: "age",
//       label: "Your Age",
//       message: "You are too young to collect social security.",
//     },
//     {
//       name: "favorite_color",
//       label: "Favorite Color",
//       message: "A favorite color is required.",
//     },
//   ]
// }
  
Promise.resolve(data)
  // this is what v.toPromise does but since validateForm is just a function
  // you can wrap it so it can be coerced into whatever shape or structure
  // you need
  .then(data => {
    const form = validateForm(data);
    
    return form.isValid
      ? Promise.resolve(form.data)
      : Promise.reject(form.errors);
  })
  .then(console.log)
  .catch(console.error)


// Pass Case
// =>
// {
//   name: "Amadaeus Blundershvlt",
//   email: "[email protected]",
//   age: 63,
//   favorite_color: "blue",
// }

// Fail Case
// =>
// [
//   {
//     name: "name",
//     label: "Full Name",
//     message: "Only a first name and last name is required.",
//   },
//   {
//     name: "email",
//     label: "Email",
//     message: "Please provide a valid email address.",
//   },
//   {
//     name: "age",
//     label: "Your Age",
//     message: "You are too young to collect social security.",
//   },
//   {
//     name: "favorite_color",
//     label: "Favorite Color",
//     message: "A favorite color is required.",
//   },
// ]