js-schema
js-schema is a new way of describing object schemas in JavaScript. It has a clean and simple syntax,
and it is capable of serializing to/from the popular JSON Schema format. The typical usecase is
decalartive object validation.
Latest release: 0.6.1 (2012/08/19)
Features
Defining a schema:
var Duck = schema({
swim : Function,
quack : Function,
age : Number.min(0).max(5),
color : ['yellow', 'brown']
});
The resulting function (Duck
) can be used to check objects against the declared schema:
var myDuck = { swim : function() {}, quack : function() {}, age : 2, color : 'yellow' },
myCat = { walk : function() {}, purr : function() {}, age : 3, color : 'black' },
animals = [ myDuck, myCat, {}, ];
console.log( Duck(myDuck) );
console.log( Duck(myCat) );
var ducks = animals.filter( Duck );
var walking = animals.filter( schema({ walk : Function }) );
It is also possible to define self-referencing data structures:
var Tree = schema({ left : [ Number, Tree ], right : [ Number, Tree ] });
console.log( Tree({ left : 3, right : 3 }) );
console.log( Tree({ left : 3, right : { left: 5, right: 5 } }) );
console.log( Tree({ left : 3, right : { left: 5, right: 's' } }) );
Usage
Include js-schema in your project with var schema = require('js-schema');
in node.js or with
<script src="js-schema.min.js"></script>
in the browser.
The first parameter passed to the schema
function describes the schema, and the return value
is a new function called validator. Then the validator can be used to check any object against
the described schema as in the example above.
There are various patterns that can be used to describe a schema. For example,
schema({n : Number})
returns a validation function which returns true when called
with an object that has a number type property called n
. This is a combination of the
object pattern and the instanceof pattern. Most of the patterns are pretty intuitive, so
reading a schema description is quite easy even if you are not familiar with js-schema.
Most patterns accept other patterns as parameters, so composition of patterns is very easy.
Extensions are functions that return validator by themselves without using the schema
function
as wrapper. These extensions are usually tied to native object constructors, like Array
,
Number
, or String
, and can be used everywhere where a pattern is expected. Examples
include Array.of(X)
, Number.min(X)
.
For serialization to JSON Schema use the toJSON()
method of any schema. For deserialization
use schema.fromJSON(json)
. JSON Schema support is still incomplete, but it can reliably
deserialize JSON Schemas generated by js-schema itself.
Patterns
Basic rules
There are 10 basic rules used for describing schemas:
Class
(where Class
is a function, and has a function type property called schema
)
matches x
if Class.schema(x) === true
.Class
(where Class
is a function) matches x
if x instanceof Class
./regexp/
matches x
if /regexp/.test(x) === true
.[object]
matches x
if x
is deep equal to object
[pattern1, pattern2, ...]
matches x
if any of the given patterns match x
.{ 'a' : pattern1, 'b' : pattern2, ... }
matches x
if pattern1
matches x.a
,
pattern2
matches x.b
, etc. For details see the object pattern subsection.primitive
(where primitive
is boolean, number, or string) matches x
if primitive === x
.null
matches x
if x
is null
or undefined
.undefined
matches anything.schema.self
references the schema returned by the last use of the schema
function.
For details see the self-referencing subsection.
The order is important. When calling schema(pattern)
, the rules are examined one by one,
starting with the first. If there's a match, js-schema first resolves the sub-patterns, and then
generates the appropriate validator function and returns it.
Example
The following example contains patterns for all of the rules. The comments
denote the number of the rules used and the nesting level of the subpatterns (indentation).
var Color = function() {}, x = { };
var validate = schema({
a : [ Color, 'red', 'blue', [[0,0,0]] ],
b : Number,
c : /The meaning of life is \d+/,
d : undefined,
e : [null, schema.self]
});
console.log( validate(x) );
validate(x)
returns true if all of these are true:
x.a
is either 'red', 'blue', an instance of the Color class,
or an array that is exactly like [0,0,0]
x.b
conforms to Number.schema (it return true if x.b instanceof Number
)x.c
is a string that matches the /The meaning of life is \d+/ regexpx
doesn't have a property called e
, or it does but it is null
or undefined
,
or it is an object that matches this schema
The object pattern
The object pattern is more complex than the others. Using the object pattern it is possible to
define optional properties, regexp properties, etc. This extra information can be encoded in
the property names.
The property names in an object pattern are always regular expressions, and the given schema
applies to instance properties whose name match this regexp. The number of expected matches can
also be specified with ?
, +
or *
as the first character of the property name. ?
means
0 or 1, *
means 0 or more, and +
means 1 or more. A single *
as a property name
matches any instance property that is not matched by other regexps.
An example of using these:
var x = { };
var validate = schema({
'name' : String,
'colou?r' : String
'?location' : String,
'*identifier-.*' : Number,
'+serialnumber-.*' : Number,
'*' : Boolean
});
assert( validate(x) === true );
Self-referencing
The easiest way to do self-referencing is using schema.self
. However, to support a more
intuitive notation (as seen in the Tree example above) there is an other way to reference
the schema that is being described. When executing this:
var Tree = schema({ left : [ Number, Tree ], right : [ Number, Tree ] });
js-schema sees in fact { left : [ Number, undefined ], right : [ Number, undefined ] }
as first
parameter, since the value of the Tree
variable is undefined when the schema function is
called. Consider the meaning of [ Number, undefined ]
according to the rules described above:
'this property must be either Number, or anything else'. It doesn't make much sense to include
'anything else' in an 'or' relation. If js-schema sees undefined
in an or relation, it assumes
that this is in fact a self-reference.
Use this feature carefully, because it may easily lead to bugs. Only use it when the return value
of the schema function is assigned to a newly defined variable.
Extensions
Numbers
There are five functions that can be used for describing number ranges: min
, max
, below
,
above
and step
. All of these are chainable, so for example Number.min(a).below(b)
matches x
if a <= x && x < b
. The Number.step(a)
matches x
if x
is a divisble by a
.
Strings
The String.of
method has three signatures:
String.of(charset)
matches x
if it is a string and contains characters that are included in charset
String.of(length, charset)
additionally checks the length of the instance and returns true only if it equals to length
.String.of(minLength, maxLength, charset)
is similar, but checks if the length is in the given interval.
charset
must be given in a format that can be directly inserted in a regular expression when
wrapped by []
. For example, 'abc'
means a character set containing the first 3 lowercase letters
of the english alphabet, while 'a-zA-C'
means a character set of all english lowercase letters,
and the first 3 uppercase letters. If charset
is undefined
then the a-zA-Z0-9
character set
is used.
Arrays
The Array.like(array)
matches x
if x instanceof Array
and it deep equals array
.
The Array.of
method has three signatures:
Array.of(pattern)
matches x
if x instanceof Array
and pattern
matches every element of x
.Array.of(length, pattern)
additionally checks the length of the instance and returns true only if it equals to length
.Array.of(minLength, maxLength, pattern)
is similar, but checks if the length is in the given interval.
Objects
Object.reference(object)
matches x
if x === object
.
Object.like(object)
matches x
if x
deep equals object
.
Functions
Function.reference(func)
matches x
if x === func
.
Future plans
Better JSON Schema support. js-schema should be able to parse any valid JSON schema and generate
JSON Schema for most of the patterns (this is not possible in general, because of patterns that hold
external references like the 'instanceof' pattern).
Error reporting. js-schema should be able to report validation errors in a meaningful way instead
of just stopping and returning false. Error handling shouldn't be the default mode of operation
because it comes at a significant performance cost and it is not needed in all usecases.
Contributing
Feel free to open an issue if you would like to help imporving js-schema or find a bug.
Installation on node.js
Using npm:
npm install js-schema
Build
To build the browser verison you will need node.js and two node.js packages: browserify
and uglifyjs installed globally (npm install -g browserify uglify-js
). build.sh
assembles a debug version using browserify and then minifies it using uglify.
License
The MIT License
Copyright (C) 2012 Gábor Molnár gabor.molnar@sch.bme.hu