Practice: Custom JS Error Types

In this practice, you will create custom JavaScript error types.

Set up

Clone the starter from the Download link at the bottom of this page.

Run npm install to install any dependencies.

Instructions

Create a ValidationError error type that inherits from the Error type. It should be thrown whenever an input is invalid.

Here's an example of how the ValidationError can be used:

class Field {
  constructor(inputName, value) {
    this.inputName = inputName;
    this.value = value;
  }
}

// When a message is passed in:
const passwordInput = new Field('Password', 'pass');
// Field { inputName: 'Password', value: 'pass' }
if (passwordInput.value === 'pass') {
  throw new ValidationError('Insecure password');
}
// throws ValidationError: Insecure password

// When a message is not passed in:
const passwordInput = new Field('Password', 10);
// Field { inputName: 'Password', value: 10 }
if (typeof passwordInput.value !== 'string') {
  throw new ValidationError();
}
// throws ValidationError: Invalid input

Implement the following in the error-types/validation-error.js file.

Create an error type called ValidationError that inherits from Error.
The first argument to the constructor method should be set to the message property of the instantiated instance. If an argument was not passed in, the message property should default to "Invalid input".

Test that your custom error type is working as intended by running the test specs in the test/validation-error-spec.js with the following command:

npm test test/validation-error-spec.js

Next, you will create a MaximumLengthExceededError error type that inherits from the ValidationError custom error type. It should be thrown whenever an input exceeds the maximum length designated for that input.

Here's an example of how the MaximumLengthExceededError can be used:

class Field {
  constructor(inputName, value, maxLength = null) {
    this.inputName = inputName;
    this.value = value;
    this.maxLength = maxLength;
  }

  changeInput(newValue) {
    if (!this.maxLength) {
      throw new MaximumLengthExceededError()
    } else if (newValue.length > this.maxLength) {
      throw new MaximumLengthExceededError(newValue.length - this.maxLength)
    }

    this.value = newValue;
  }
}

// When no maximum length is specified:
const nameInput = new Field('Name', 'Zelda');
// Field { inputName: 'Name', value: 'Zelda', maxLength: null }
nameInput.changeInput('Sheik');
// throws MaximumLengthExceededError: Maximum length exceeded

// When maximum length is specified and is exceeded:
const nameInput = new Field('Name', 'Zelda', 5);
// Field { inputName: 'Name', value: 'Zelda', maxLength: 5 }
nameInput.changeInput("Ganondorf");
// throws MaximumLengthExceededError: Maximum length exceeded by 4

// When maximum length is specified and is not exceeded:
const nameInput = new Field('Name', 'Zelda', 5); 
// Field { inputName: 'Name', value: 'Zelda', maxLength: 5 }
nameInput.changeInput("Sheik");
// does not throw an error

Implement the following in the error-types/maximum-length-exceeded-error.js file.

Create an error type called MaximumLengthExceededError that inherits from ValidationError.
The first argument to the constructor method should represent the difference in the maximum length and actual length of the input. The message property of the instantiated instance should be set to "Maximum length exceeded by ${excessLength}" if there is a first argument. If there isn't a first argument passed in, the message property should default to "Maximum length exceeded".

Test that your custom error type is working as intended by running the test specs in the test/maximum-length-exceeded-error-spec.js with the following command:

npm test test/maximum-length-exceeded-error-spec.js

horsemandotpy/practice-for-week-04-custom-error-types

Practice: Custom JS Error Types

Set up

Instructions