tcomb
Advanced tools
Package description
The tcomb npm package is a library for Node.js and the browser which allows you to check the types of JavaScript values at runtime with a simple and concise syntax. It is useful for enforcing type safety, defining domain models, and creating composable and reusable type checkers.
Type Checking
This feature allows you to define a structure with specific types and create instances that adhere to those types.
const t = require('tcomb');
const Person = t.struct({ name: t.String, age: t.Number });
const person = Person({ name: 'Giulio', age: 43 });Function Argument Validation
This feature enables you to validate function arguments to ensure they are of the expected type.
const t = require('tcomb');
function sum(a, b) {
t.Number(a);
t.Number(b);
return a + b;
}
sum(1, 2);Subtyping
This feature allows you to create subtypes based on existing types with additional constraints.
const t = require('tcomb');
const Positive = t.subtype(t.Number, n => n >= 0);
const positiveNumber = Positive(10);Refinement
This feature is similar to subtyping but is specifically for refining types to a more specific subset.
const t = require('tcomb');
const Integer = t.refinement(t.Number, n => n % 1 === 0);
const integerNumber = Integer(42);Enums
This feature allows you to define a set of constants and ensure values match one of those constants.
const t = require('tcomb');
const Role = t.enums({ Admin: 'Admin', User: 'User' });
const userRole = Role('User');Prop-types is a library for React that is used to document the intended types of properties passed to components. It is similar to tcomb in that it provides runtime type checking, but it is specifically tailored for React's component props.
io-ts is a TypeScript runtime type system for IO decoding/encoding. It is similar to tcomb in providing runtime type checking and validation, but it leverages TypeScript's type system for added compile-time safety.
Joi is an object schema description language and validator for JavaScript objects. It provides a powerful and expressive way to define and validate data structures. It is similar to tcomb in terms of validation capabilities but has a different API and is often used for validating API input.
Ajv is a JSON schema validator. It validates data against JSON Schema standards and is similar to tcomb in terms of validation. However, it uses a JSON-based schema definition rather than a programmatic API.
Readme
JavaScript types and combinators
tcomb is a library which allows you to check the types of JavaScript values at runtime with a simple syntax. It is great for checking external input, for testing and for adding safety to your internal code. Bonus points:
This library provides several type combinators and a built-in assert function you can use. When an assertion fails in the browser this function starts the debugger so you can inspect the stack and find what's wrong. The debugger starts only once after the first failed assert.
Let's build a product
var Product = struct({
name: Str, // a REQUIRED string
description: maybe(Str), // an OPTIONAL string (can be `null`)
homepage: Url, // a SUBTYPE string representing a URL
shippings: list(Shipping), // a LIST of shipping methods
category: Category, // a string in [Audio, Video] (ENUM)
price: union(Num, Price), // price expressed in dollars OR in another currency (UNION)
dim: tuple([Num, Num]) // width x height (TUPLE)
});
var Url = subtype(Str, function (s) {
return s.indexOf('http://') === 0;
});
var Shipping = struct({
description: Str,
cost: Num
});
var Category = enums({
Audio: 0,
Video: 1
});
var Price = struct({
currency: Str,
amount: Num
});
var ipod = new Product({
name: 'iPod',
description: 'Engineered for maximum funness.',
homepage: 'http://www.apple.com/ipod/',
shippings: [{
description: 'Shipped to your door, free.',
cost: 0
}],
category: 'Audio',
price: {currency: 'EUR', amount: 100},
dim: [2.4, 4.1]
});
Node
npm install tcomb
var t = require('tcomb');
Browser
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>tcomb setup</title>
<!--[if lt IE 9]>
<script src="shims/json2.js"></script>
<script src="shims/es5-shim.min.js"></script>
<script src="shims/es5-sham.min.js"></script>
<script src="shims/html5shiv.min.js"></script>
<![endif]-->
<script type="text/javascript" src="tcomb.js"></script>
</head>
<body>
<script type="text/javascript">
console.log(t);
</script>
</body>
</html>
Some ES5 methods
Array#forEach()
Array#map()
Array#some()
Array#every()
Object#freeze()
Object#keys()
Run
mocha
on the project root.
A type is a function T such that
T has signature T(values, [mut]) where values depends on the nature of T and the optional boolean arg mut makes the instance mutable (default false)T is idempotent: new T(new T(values)) "equals" new T(values)T owns a static function T.is(x) returning true if x is a instance of TNote: 2. implies that T can be used as a default JSON decoder
Used internally to define JavaScript native types:
null and undefinedExample
Str.is('a'); // => true
Nil.is(0); // => false
Defines a struct like type.
props hash field name -> typename optional string useful for debuggingExample
// define a struct with two numerical props
var Point = struct({
x: Num,
y: Num
});
Methods are defined as usual
Point.prototype.toString = function () {
return '(' + this.x + ', ' + this.y + ')';
};
Building an instance is simple as
"use strict";
var p = new Point({x: 1, y: 2});
p.x = 2; // => TypeError, p is immutable
p = new Point({x: 1, y: 2}, true); // now p is mutable
p.x = 2; // ok
Some meta informations are stored in a meta hash
Point.meta = {
kind: 'struct',
props: props,
name: name
};
is(x)
Returns true if x is an instance of Point.
Point.is(p); // => true
update(instance, updates, [mut])
Returns an instance with changed props, without modify the original.
Point.update(p, {x: 3}); // => new Point({x: 3, y: 2})
Defines a types union.
types array of typesname optional string useful for debuggingExample
var Circle = struct({
center: Point,
radius: Num
});
var Rectangle = struct({
bl: Point, // bottom left vertex
tr: Point // top right vertex
});
var Shape = union([
Circle,
Rectangle
]);
// in order to use Shape as constructor `dispatch(values) -> Type`
// must be implemented
Shape.dispatch = function (values) {
assert(Obj.is(values));
return values.hasOwnProperty('center') ?
Circle :
Rectangle;
};
var shape = new Shape({center: {x: 1, y: 2}, radius: 10});
Some meta informations are stored in a meta hash
Shape.meta = {
kind: 'union',
types: types,
name: name
};
is(x)
Returns true if x belongs to the union.
Shape.is(new Circle([p, 10])); // => true
Same as union([Nil, type]).
var MaybeStr = maybe(Str);
MaybeStr.is('a'); // => true
MaybeStr.is(null); // => true
MaybeStr.is(1); // => false
Some meta informations are stored in a meta hash
MaybeStr.meta = {
kind: 'maybe',
type: type,
name: name
};
Defines an enum of strings.
var Direction = enums({
North: 0,
East: 1,
South: 2,
West: 3
});
Some meta informations are stored in a meta hash
Direction.meta = {
kind: 'enums',
map: map,
name: name
};
is(x)
Returns true if x belongs to the enum.
Direction.is('North'); // => true
Defines a tuple whose coordinates have the specified types.
var Args = tuple([Num, Num]);
var a = new Args([1, 2]);
Some meta informations are stored in a meta hash
Args.meta = {
kind: 'tuple',
types: types,
name: name
};
is(x)
Returns true if x belongs to the tuple.
Args.is([1, 2]); // => true
Args.is([1, 'a']); // => false, second element is not a Num
Args.is([1, 2, 3]); // => false, too many elements
update(instance, index, element, [mut])
Returns an instance without modifying the original.
Args.update(a, 0, 2); // => [2, 2]
Defines a subtype of an existing type.
var Int = subtype(Num, function (n) {
return n === parseInt(n, 10);
});
// points of the first quadrant
var Q1Point = subtype(Point, function (p) {
return p.x >= 0 && p.y >= 0;
});
// constructor usage
var p = new Q1Point({x: -1, y: -2}); // => fail!
Some meta informations are stored in a meta hash
Int.meta = {
kind: 'subtype',
type: type,
predicate: predicate,
name: name
};
is(x)
Returns true if x belongs to the subtype.
Int.is(2); // => true
Int.is(1.1); // => false
Defines an array where all elements are of type type.
var Path = list(Point);
// costructor usage
var path = new Path([
{x: 0, y: 0},
{x: 1, y: 1}
]);
Some meta informations are stored in a meta hash
Path.meta = {
kind: 'list',
type: type,
name: name
};
is(x)
Returns true if x belongs to the list.
Path.is([{x: 0, y: 0}, {x: 1, y: 1}]); // => true
Useful methods
Return an instance without modifying the original.
Path.append(path, element, [mut]);
Path.prepend(path, element, [mut]);
Path.update(path, index, element, [mut]);
Path.remove(path, index, [mut]);
Path.move(path, from, to, [mut]);
fail(message)
assert(guard, [message])
// make properties immutables unless `unless` is `true`
freeze(obj_or_arr, [unless])
// adds the properties of `y` to `x`. If `overwrite` is falsy
// and a property already exists, throws an error
mixin(x, y, [overwrite])
// array manipulation
append(arr, element);
prepend(arr, element);
update(arr, index, element);
remove(arr, index);
move(arr, from, to);
var Point3D = struct(mixin(Point.meta.props, {
z: Num
}));
var p = new Point3D({x: 1, y: 2, z: 3});
var c = new Circle({center: {x: 1, y: 2}, radius: 10});
// translate x by 1
var c2 = Circle.update(c, {
center: Point.update(c.center, {
x: c.center.x + 1
})
});
// (json, T, mut) -> instance of T
function decode(json, T, mut) {
if (T.fromJSON) {
return T.fromJSON(json, mut);
}
switch (T.meta.kind) {
case 'struct' :
var values = {};
var props = T.meta.props;
for (var prop in props) {
if (props.hasOwnProperty(prop)) {
values[prop] = decode(json[prop], props[prop], mut);
}
}
return new T(values, mut);
case 'union' :
assert(Func.is(T.dispatch));
return decode(json, T.dispatch(json), mut);
case 'maybe' :
return Nil.is(json) ? undefined : decode(json, T.meta.type, mut);
case 'tuple' :
return freeze(json.map(function (x, i) {
return decode(x, T.meta.types[i], mut);
}, mut));
case 'subtype' :
var x = decode(json, T.meta.type, mut);
assert(T.meta.predicate(x));
return x;
case 'list' :
return freeze(json.map(function (x) {
return decode(x, T.meta.type, mut);
}), mut);
default :
return json;
}
};
Copyright (C) 2014 Giulio Canti - Released under the MIT License.
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
FAQs
Type checking and DDD for JavaScript
The npm package tcomb receives a total of 1,348,425 weekly downloads. As such, tcomb popularity was classified as popular.
We found that tcomb demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 1 open source maintainer collaborating on the project.
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