rttc

rttc

Runtime (recursive) type-checking for JavaScript.

Installation

$ npm install rttc --save

Quick Start

var rttc = require('rttc');

rttc.coerce({ firstName: 'string'}, {firstName: 45});
// => { firstName: "45" }

rttc.coerce({ firstName: 'string'}, {something: 'totally incorrect'});
// => { firstName: "" }
// (when confronted with something totally weird, `.coerce()` returns the "base value" for the type)

rttc.validate({ firstName: 'string'}, {something: 'totally incorrect'});
// throws error

rttc.validate({ firstName: 'string'}, {firstName: 45});
// => "45"
// (when confronted with minor differences, `.validate()` coerces as needed to make stuff fit)

rttc.validateStrict({ firstName: 'string'}, {firstName: 45});
// throws error
// (`.validateStrict()` demands a value that is precisely the correct type)

rttc.validateStrict({ firstName: 'string'}, {firstName: '45'});
// does not throw, returns undefined

Philosophy

All of the validation and coercion strategies used in this modules are recursive through the keys of plain old JavaScript objects and the indices of arrays.

Coercion vs. Validation

• .validateStrict() throws if the provided value is not the right type (recursive).
• .validate() either returns a (potentially "lightly" coerced) version of the value that was accepted, or it throws. The "lightly" coerced value turns "3" into 3, "true" into true, -4.5 into "-4.5", etc.
• .coerce() ALWAYS returns an acceptable version of the value, even if it has to mangle it to get there (i.e. by using the "base value" for the expected type.)

Base values

• For "string", base value is ""
• For "number", base value is 0
• For "boolean", base value is false
• For any "dictionary" ({}), base value is {}, with whatever keys are expected (recursive)
• For a generic "array" ([]), base value is [], with a single archetypal item matching the expectation (recursive)

Edge cases

• undefined will always be coerced to the base value of the expected type.
• null is never valid.
• NaN is never valid.
• Infinity is never valid.
• -Infinity is never valid.

Dictionaries

• Dictionaries (i.e. plain old JavaScript objects like {}) in type schemas can be infinitely nested. Type validation and coercion will proceed through the nested objects recursively.

{
  id: 'number',
  name: 'string',
  isAdmin: 'boolean',
  mom: {
    id: 'number',
    name: 'string',
    occupation: {
      title: 'string',
      workplace: 'string'
    }
  }
}

When validating against a dictionary schema with at least one key, extra keys in the actual value will be stripped out. If the dictionary schema is empty, all actual keys will be left alone.

Arrays

• Arrays in type schemas must be homogeneous and have exactly one item; that is, if you want to validate an array, you only need to provide the type/schema for the first item in the array, e.g.:

[
  {
    id: 'number',
    name: 'string',
    email: 'string',
    age: 'number',
    isAdmin: 'boolean',
    favoriteColors: ['string'],
    friends: [
      {
        id: 'number',
        name: 'string'
      }
    ]
  }
]

Usage

rttc.infer(value)

Infer the type/schema of the provided value.

require('rttc').infer(false);
// => 'boolean'

require('rttc').infer(0);
// => 'number'

require('rttc').infer({
  foo: 'bar'
});
// => { foo: 'string' }

require('rttc').infer({
  foo: 'whatever',
  bar: { baz: true }
});
// => { foo: 'string', bar: { baz: 'boolean' } }

require('rttc').infer([{
  foo: ['bar']
}]);
// => [{ foo: ['string'] }]

require('rttc').infer({
  user: {
    friends: [{
      name: 'Lenny',
      age: 77
    }]
});
// =>
/*
{
  user: {
    friends: [{
      name: 'Lenny',
      age: 77
    }]
}
*/

rttc.validate(expected, actual)

rttc.validate('string', 'foo');
// => 'foo'

rttc.validate('number', 4.5);
// => 4.5

rttc.validate('boolean', true);
// => true

rttc.validate('string', -2);
// => '-2'

rttc.validate('string', false);
// => 'false'

rttc.validate('number', '3');
// => 3

rttc.validate('boolean', 'true');
// => true

rttc.validate({
  user: {
    friends: [{
      name: 'Lenny',
      age: 77
    }]
}, {
  user: {
    friends: [{
      name: 'Lenny',
      age: '77'
    }]
  }
});
// =>
/*
{
  user: {
    friends: [{
      name: 'Lenny',
      age: 77
    }]
  }
}
 */

If value cannot be properly coerced, throws error with code=E_INVALID_TYPE:

rttc.validate('number', 'asdf');
// throws E_INVALID_TYPE

rttc.coerce(expected, actual)

rttc.coerce('string', 'foo');
// => 'foo'

rttc.coerce('number', 4.5);
// => 4.5

rttc.coerce('boolean', true);
// => true

rttc.coerce('string', -2);
// => '-2'

rttc.coerce('string', false);
// => 'false'

rttc.coerce('number', '3');
// => 3

rttc.coerce('boolean', 'true');
// => true

If value can't be properly coerced, the "base value" for the type will be used:

rttc.coerce('number', 'asdf');
// => 0

rttc.coerce('boolean', 'asdf');
// => false

rttc.coerce({
  user: {
    friends: [{
      name: 'Lenny',
      age: 77
    }]
}, 'err... some dude who\'s friends with lenny?');
// =>
/*
{
  user: {
    friends: [{
      name: 'Lenny',
      age: 77
    }]
  }
}
 */