Interface Validator

Validate JSON objects with TypeScript-like interface specifications.

Installation

npm install interface-validator

Usage

Specify TypeScript-like interface definition:

const Product = {
  name: 'string!',
  price: 'number!',
  'description?': 'string'
};

import {getMismatchedFields, validate} from 'interface-validator';

const invalidItem = {
  name: '',
  price: '100'
}
const mismatched = getMismatchedFields(invalidItem, Product);
const isValid = valid(invalidItem, Product);
// Result:
// mismatched = ['name']
// isValid = false
// item = {
//   name: undefined,
//   price: 100
// }

Types

Values are checked by this simple statement:

typeof value === specType

Supported types include:

• string
• number
• boolean
• object
• nested interface

Nested interface definition is supported. E.g

const Product = {
  name: 'string!',
  price: {
    value: 'number!',
    currency: 'string!'
  },
  'description?': 'string'
}

Type enforcing: You can append ! to the type names to indicate you want to cast the values to the specified types before checking. The tested object's fields will be modified to contain the typecasted values. Refer to the above example to see the effect.

There are some special cases:

• number!: if the converted value is NaN or Infinity, the value will be set to undefined
• boolean!: only 'true' and 'false' will be converted to boolean. All other values will be set to undefined.
• string!: if the value is empty string, it will be set to undefined.

Optional fields are indicated with a question mark after the field name, like 'description?';

When to use this

There are many powerful validation libraries out there. This library is not meant to rival their functionalities. Instead, this is intended to perform very simple run-time interface checks.

In TypeScript you can put compile-time contract on JSON objects using interface but they are stripped away at run-time. So there is no way to perform obj instanceof Interface even when using TypeScript. Not to mention plain Javascript where there is no concept of an interface.

So when you want to do just object instanceof Interface, use this library. Any slightly more complex cases should be handled by more sophisticated libraries.

Contribute

Report issues or submit pull requests.

Tests

npm test