embarq/index.html

## index.html
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>DOM task: Form model</title>
  <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css" integrity="sha384-Vkoo8x4CGsO3+Hhxv8T/Q5PaXtkKtu6ug5TOeNV6gBiFeWPGFN9MuhOf23Q9Ifjh" crossorigin="anonymous">

  <style>
    .app-container {
      width: 420px;
      padding-top: 3rem;
    }
  </style>
</head>
<body>
  <div class="container app-container">
    <form action="">
      <p class="form-group px-3">
        <label for="email-control">Email</label>
        <input id="email-control" type="email" placeholder="example@org.com" class="form-control" />
      </p>
      <p class="form-group px-3">
        <label for="username-control">Username</label>
        <input type="text" id="username-control" class="form-control" />
      </p>
    </form>
  </div>
  <script src="main.js"></script>
</body>
</html>

## main.js
class EventEmitter {
  constructor() {
    this.handlers = [];
  }
  subscribe(eventHandler) {
    this.handlers.push(eventHandler);
  }
  emit(data) {
    this.handlers.forEach(handler => handler(data));
  }
}

class Validator {
  validate() {
    throw new Error('Not implemented');
  }
}

class RequiredValidator extends Validator {
  validate(value) {
    return value != null && (typeof value === 'string' && value.trim().length > 0);
  }
}

class MinLengthValidator extends Validator {
  constructor(minValue) {
    super();

    if (!Number.isFinite(minValue)) {
      throw new Error('minValue is required argument');
    }

    this.minValue = minValue;
  }

  validate(value) {
    return value.length > this.minValue;
  }
}

class FormControl {
  constructor(id, initialValue = '', validators) {
    this.value = initialValue;
    this.validators = validators;
    this.status = false;
    this.statusChange = new EventEmitter();

    // TODO: show hints about validation state
    const inputElem = document.getElementById(id);
    inputElem.addEventListener('change', (event) => {
      this.status = this.validators.every(validator => {
        if (!(validator instanceof Validator)) {
          throw new Error('Invalid validator');
        }

        return validator.validate(event.target.value);
      });
      this.statusChange.emit(this.status);
    });

    this.statusChange.subscribe(status => {
      if (status === false) {
        const hintElem = document.createElement('p');
        hintElem.className = 'text-danger';
        hintElem.innerText = 'Value is invalid';
        hintElem.id = 'hint-for-' + inputElem.id;
        inputElem.parentElement.appendChild(hintElem);
        inputElem.classList.toggle('is-invalid');
      } else {
        const hintElem = inputElem.parentElement.querySelector('#hint-for-' + inputElem.id);
        if (hintElem != null) {
          inputElem.classList.toggle('is-invalid');
          hintElem.remove();
        }
      }
    });
  }
}

class FormGroup {
  constructor(id, controls) {
    this.status = false;
    this.statusChange = new EventEmitter();
    this.controlsStatus = { };

    for (let control of controls) {
      control.statusChange.subscribe(status => {
        this.controlsStatus[control.id] = status;

        this.status = Object.values(this.controlsStatus).every(controlStatus => (controlStatus === true));
        this.statusChange.emit(this.status);
      });
    }
  }
}

window.addEventListener('DOMContentLoaded', () => {
  const registerForm = new FormGroup('', [
    new FormControl('email-control', '', [
      new RequiredValidator()
    ]),
    new FormControl('username-control', '', [
      new RequiredValidator(),
      new MinLengthValidator(3)
    ])
  ]);

  registerForm.statusChange.subscribe((formStatus) => {
    console.log('Register form status is', formStatus);
  });

  // const emailControl = new FormControl('email-control', '', [
  //   new RequiredValidator()
  // ]);
  // const usernameControl = new FormControl('username-control', '', [
  //   new RequiredValidator(),
  //   new MinLengthValidator(3)
  // ]);

  // emailControl.statusChange.subscribe(status => {
  //   console.log('Email control status is', status);
  // });

  // usernameControl.statusChange.subscribe(status => {
  //   console.log('Username control status is', status);
  // });
})
	<!DOCTYPE html>
	<html lang="en">
	<head>
	<meta charset="UTF-8">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<meta http-equiv="X-UA-Compatible" content="ie=edge">
	<title>DOM task: Form model</title>
	<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css" integrity="sha384-Vkoo8x4CGsO3+Hhxv8T/Q5PaXtkKtu6ug5TOeNV6gBiFeWPGFN9MuhOf23Q9Ifjh" crossorigin="anonymous">

	<style>
	.app-container {
	width: 420px;
	padding-top: 3rem;
	}
	</style>
	</head>
	<body>
	<div class="container app-container">
	<form action="">
	<p class="form-group px-3">
	<label for="email-control">Email</label>
	<input id="email-control" type="email" placeholder="example@org.com" class="form-control" />
	</p>
	<p class="form-group px-3">
	<label for="username-control">Username</label>
	<input type="text" id="username-control" class="form-control" />
	</p>
	</form>
	</div>
	<script src="main.js"></script>
	</body>
	</html>
	class EventEmitter {
	constructor() {
	this.handlers = [];
	}
	subscribe(eventHandler) {
	this.handlers.push(eventHandler);
	}
	emit(data) {
	this.handlers.forEach(handler => handler(data));
	}
	}

	class Validator {
	validate() {
	throw new Error('Not implemented');
	}
	}

	class RequiredValidator extends Validator {
	validate(value) {
	return value != null && (typeof value === 'string' && value.trim().length > 0);
	}
	}

	class MinLengthValidator extends Validator {
	constructor(minValue) {
	super();

	if (!Number.isFinite(minValue)) {
	throw new Error('minValue is required argument');
	}

	this.minValue = minValue;
	}

	validate(value) {
	return value.length > this.minValue;
	}
	}

	class FormControl {
	constructor(id, initialValue = '', validators) {
	this.value = initialValue;
	this.validators = validators;
	this.status = false;
	this.statusChange = new EventEmitter();

	// TODO: show hints about validation state
	const inputElem = document.getElementById(id);
	inputElem.addEventListener('change', (event) => {
	this.status = this.validators.every(validator => {
	if (!(validator instanceof Validator)) {
	throw new Error('Invalid validator');
	}

	return validator.validate(event.target.value);
	});
	this.statusChange.emit(this.status);
	});

	this.statusChange.subscribe(status => {
	if (status === false) {
	const hintElem = document.createElement('p');
	hintElem.className = 'text-danger';
	hintElem.innerText = 'Value is invalid';
	hintElem.id = 'hint-for-' + inputElem.id;
	inputElem.parentElement.appendChild(hintElem);
	inputElem.classList.toggle('is-invalid');
	} else {
	const hintElem = inputElem.parentElement.querySelector('#hint-for-' + inputElem.id);
	if (hintElem != null) {
	inputElem.classList.toggle('is-invalid');
	hintElem.remove();
	}
	}
	});
	}
	}

	class FormGroup {
	constructor(id, controls) {
	this.status = false;
	this.statusChange = new EventEmitter();
	this.controlsStatus = { };

	for (let control of controls) {
	control.statusChange.subscribe(status => {
	this.controlsStatus[control.id] = status;

	this.status = Object.values(this.controlsStatus).every(controlStatus => (controlStatus === true));
	this.statusChange.emit(this.status);
	});
	}
	}
	}

	window.addEventListener('DOMContentLoaded', () => {
	const registerForm = new FormGroup('', [
	new FormControl('email-control', '', [
	new RequiredValidator()
	]),
	new FormControl('username-control', '', [
	new RequiredValidator(),
	new MinLengthValidator(3)
	])
	]);

	registerForm.statusChange.subscribe((formStatus) => {
	console.log('Register form status is', formStatus);
	});

	// const emailControl = new FormControl('email-control', '', [
	// new RequiredValidator()
	// ]);
	// const usernameControl = new FormControl('username-control', '', [
	// new RequiredValidator(),
	// new MinLengthValidator(3)
	// ]);

	// emailControl.statusChange.subscribe(status => {
	// console.log('Email control status is', status);
	// });

	// usernameControl.statusChange.subscribe(status => {
	// console.log('Username control status is', status);
	// });
	})