More expressive

sample.js

/* Original code from https://seanbarry.dev/posts/switch-true-pattern:
switch (true) {
  case !isDefined(user):
    throw new Error("User must be defined.");
  case !isString(user.firstName):
    throw new Error("User's first name must be a string");
  case !isValidEmail(user.email):
    throw new Error("User's email address must be a valid email address");
  case !isValidPhoneNumber(user.number):
    throw new Error("User's phone number must be a valid phone number");
  // any number of other validation cases here
  default:
    return user;
}
*/

function isDefined(user) {
  return true;
}

function isString(user) {
  return true;
}

function isValidEmail(user) {
  return true;
}

function isValidPhoneNumber(user) {
  return true;
}

let user = {};
let validation_cases = [
    {
        check: isDefined,
        error_message: "User must be defined.",
    },
    {
        check: isString,
        error_message: "User's first name must be a string",
    },
    {
        check: isValidEmail,
        error_message: "User's email address must be a valid email address",
    },
    {
        check: isValidPhoneNumber,
        error_message: "User's phone number must be a valid phone number",
    },
];

function validate(validation) {
    if (validation.check(user)) { return true; } else { throw new Error(validation.error_message);};
}

let passed = validation_cases.every(validate);
console.log("passed: ", passed);