A little JavaScript library
for asserting types
and values.
Writing explicit conditions
in your functions
to check arguments
and throw exceptions
is a task that
swiftly becomes tiresome
and adds complexity
to your codebase.
The purpose of check-types.js
is to remove this burden
from JavaScript application developers
in an efficient and robust manner,
abstracted by a simple API.
20 kb unminified with comments, 5.7 kb minified, 2.1 kb minified + gzipped.
Via npm:
npm i check-types --save
Or if you just want the git repo:
git clone git@gitlab.com:philbooth/check-types.js.git
If you're into
other package managers,
it is also available
from Bower, Component and Jam.
If you are running in
Node.js,
Browserify
or another CommonJS-style
environment,
you can require
check-types like so:
var check = require('check-types');
It also the supports
the AMD-style format
preferred by Require.js.
If you are
including check-types.js
with an HTML <script> tag,
or neither of the above environments
are detected,
it will export the interface globally as check.
Once you've loaded the library
in your application,
a whole bunch of functions are available
to call.
Most of the functions
are predicates,
which can be executed
in a number of different contexts:
check.xxx(thing):
These functions are basic predicates,
returning true or false
depending on the type and value of thing.
check.not.xxx(thing):
The not modifier
negates predicates,
returning true if the predicate returns false
and false if the predicate returns true.
It is also itself a function,
which simply returns
the negation of
its argument.
check.maybe.xxx(thing):
The maybe modifier
tweaks predicates to
return true if thing is null or undefined,
otherwise their normal result
is returned.
It is also itself a function,
which returns true
when its argument is null or undefined,
otherwise it returns its argument.
check.assert.xxx(thing, message):
The assert modifier
changes predicates
to throw when their result is false,
otherwise it returns thing.
It can be applied
to the not and maybe modifiers
using the forms
check.assert.not.xxx(thing, message) and
check.assert.maybe.xxx(thing, message).
It is also itself a function,
which simply throws
when its argument is false.
check.array.of.xxx(thing):
The array.of modifier
first checks that
it is operating on an array
and then applies
the modified predicate
to each item
of the array.
If the predicate fails
for any item,
it returns false,
otherwise it returns true.
It can also be prefixed
by other modifiers,
so check.maybe.array.of,
check.not.array.of,
check.assert.array.of,
check.assert.maybe.array.of and
check.assert.not.array.of
all work
as you would expect
them to.
check.arrayLike.of.xxx(thing):
The arrayLike.of modifier
is synonymous with array.of,
except it operates on array-like objects.
check.iterable.of.xxx(thing):
The iterable.of modifier
is synonymous with array.of,
except it operates on iterables.
check.object.of.xxx(thing):
The object.of modifier
is synonymous with array.of,
except it operates on an object's properties.
Additionally, there are some batch operations
to help you apply predicates
to each value
of an array or object.
These are implemented bycheck.map,check.any andcheck.all.
check.equal(thing, thang):
Returns true
if thing === thang,
false otherwise.
check.null(thing):
Returns true
if thing is null,
false otherwise.
check.undefined(thing):
Returns true
if thing is undefined,
false otherwise.
check.assigned(thing):
Returns true
if thing is not
null or undefined,
false otherwise.
check.primitive(thing):
Returns true
if thing is a primitive type,
false otherwise.
Primitive types are
null, undefined, booleans, numbers, strings and symbols.
check.hasLength(thing, value):
Returns true
if thing has a length property
that equals value,
false otherwise.
check.string(thing):
Returns true
if thing is a string,
false otherwise.
check.emptyString(thing):
Returns true
if thing is the empty string,
false otherwise.
check.nonEmptyString(thing):
Returns true
if thing is a non-empty string,
false otherwise.
check.contains(thing, substring):
Returns true
if thing is a string
that contains substring,
false otherwise.
check.match(thing, regex):
Returns true
if thing is a string
that matches regex,
false otherwise.
check.number(thing):
Returns true
if thing is a number,
false otherwise.
Note that
NaN,
Number.POSITIVE_INFINITY and
Number.NEGATIVE_INFINITY
are not considered numbers here.
check.integer(thing):
Returns true
if thing is an integer,
false otherwise.
check.zero(thing):
Returns true
if thing is zero,
false otherwise.
check.infinity(thing):
Returns true
if thing is positive or negative infinity,
false otherwise.
check.greater(thing, value):
Returns true if thing is a number
greater than value,
false otherwise.
check.greaterOrEqual(thing, value):
Returns true if thing is a number
greater than or equal to value,
false otherwise.
check.less(thing, value):
Returns true if thing is a number
less than value,
false otherwise.
check.lessOrEqual(thing, value):
Returns true if thing is a number
less than or equal to value,
false otherwise.
check.between(thing, a, b):
Returns true if thing is a number
between a and b
(excluding a and b),
false otherwise.
The arguments a and b
may be in any order,
it doesn't matter
which is greater.
check.inRange(thing, a, b):
Returns true if thing is a number
in the range a .. b
(including a and b),
false otherwise.
The arguments a and b
may be in any order,
it doesn't matter
which is greater.
check.positive(thing):
Returns true if thing is a number
greater than zero,
false otherwise.
check.negative(thing):
Returns true
if thing is a number
less than zero,
false otherwise.
check.odd(thing):
Returns true
if thing is an odd number,
false otherwise.
check.even(thing):
Returns true
if thing is an even number,
false otherwise.
check.boolean(thing):truething is a boolean,false otherwise.check.object(thing):
Returns true
if thing is a plain-old JavaScript object,
false otherwise.
check.emptyObject(thing):
Returns true
if thing is an empty object,
false otherwise.
check.nonEmptyObject(thing):
Returns true
if thing is a non-empty object,
false otherwise.
check.instanceStrict(thing, prototype):
Returns true
if thing is an instance of prototype,
false otherwise.
check.instance(thing, prototype):
Returns true
if thing is an instance of prototype,
false otherwise.
Falls back to testing
constructor.name and Object.prototype.toString
if the instanceof test fails.
check.like(thing, duck):
Duck-typing checker.
Returns true
if thing has all of the properties of duck,
false otherwise.
check.array(thing):
Returns true
if thing is an array,
false otherwise.
check.emptyArray(thing):
Returns true
if thing is an empty array,
false otherwise.
check.nonEmptyArray(thing):
Returns true
if thing is a non-empty array,
false otherwise.
check.arrayLike(thing):
Returns true
if thing has a numeric length property,
false otherwise.
check.iterable(thing):
Returns true
if thing implements the iterable protocol,
false otherwise.
In pre-ES6 environments,
this predicate falls back
to arrayLike behaviour.
check.includes(thing, value):
Returns true
if thing includes value,
false otherwise.
check.date(thing):truething is a valid date,false otherwise.check.function(thing):truething is a function,false otherwise.check.not(value):
Returns the negation
of value.
check.not.xxx(...):
Returns the negation
of the predicate.
check.maybe(value):
Returns true
if value is null or undefined,
otherwise it returns value.
check.maybe.xxx(...):
Returns true
if thing is null or undefined,
otherwise it propagates
the return value
from its predicate.
check.array.of.xxx(value):
Returns true
if value is an array
and the predicate is true
for every item.
Also works with the not and maybe modifiers.
check.arrayLike.of.xxx(thing):
The arrayLike.of modifier
is synonymous with array.of,
except it operates on array-like objects.
check.iterable.of.xxx(thing):
The iterable.of modifier
is synonymous with array.of,
except it operates on iterables.
check.object.of.xxx(thing):
The object.of modifier
is synonymous with array.of,
except it operates on an object's properties.
check.assert(value, message, ErrorType):
Throws a TypeError
if value is falsy,
otherwise it returns value.
message and ErrorType
are optional arguments
that control
the message and type
of the thrown error object.
check.assert.xxx(...):
Throws a TypeError
if the predicate returns false,
otherwise it returns the subject value.
The last two arguments
are an optional message and error type
that control
the message and type
of the thrown error object.
Also works with the not, maybe and ...of modifiers.
check.map(things, predicates):
Maps each value from the things array or object
to the corresponding predicate
and returns the array or object of results.
Passing a single predicate
instead of an array or object
maps all of the values
to the same predicate.
check.all(results):
Returns true
if all the result values are true
in an array or object
returned by map.
check.any(results):
Returns true
if any result value is true
in an array or object
returned by map.
check.even(3);
// Returns false
check.not.even(3);
// Returns true
check.maybe.even(null);
// Returns true
check.assert.like({ foo: 'bar' }, { baz: 'qux' });
// Throws `new TypeError('Invalid type')`
check.assert.not.like({ foo: 'bar' }, { baz: 'qux' });
// Doesn't throw, returns `{ foo: 'bar' }`
check.assert.maybe.like(undefined, { foo: 'bar' });
// Doesn't throw, returns `undefined`
check.assert(myFunction(), 'Something went wrong', CustomError);
// Throws `new CustomError('Something went wrong')` if myFunction returns `false`
check.map([ 'foo', 'bar', '' ], check.nonEmptyString);
// Returns [ true, true, false ]
check.map({
foo: 2,
bar: { baz: 'qux' }
}, {
foo: check.odd,
bar: { baz: check.nonEmptyString }
});
// Returns { foo: false, bar: { baz: true } }
check.all(
check.map(
{ foo: 0, bar: '' },
{ foo: check.number, bar: check.string }
)
);
// Returns true
check.any(
check.map(
[ 1, 2, 3, '' ],
check.string
)
);
// Returns true
Yes!
Thanks to @idchlife,
type definitions were added
to DefinitelyTyped.
You can add them to your project
via npm:
npm i @types/check-types --save-dev
As of version 2.0,
this library no longer supports ES3.
That means you can't use it
in IE 7 or 8.
Everywhere else should be fine.
If those versions of IE
are important to you,
worry not!
The 1.x versions
all support old IE
and any future 1.x versions
will adhere to that too.
See the releases
for more information.
Breaking changes
were made to the API
in version 8.0.0.
Specifically,
the apply batch operation was removed
and map was instead changed
to work with both arrays and objects,
to simplify the API surface.
See the history
for more details.
Breaking changes
were made to the API
in version 7.0.0.
Specifically,
the instance predicate
was renamed to instanceStrict
and the builtIn and userDefined predicates
were combined to form
a new instance predicate.
See the history
for more details.
Breaking changes
were made to the API
in version 6.0.0.
Specifically,
the either modifier was removed.
Instead,
calling code can use
the any function,
or simply express the boolean logic
in JS.
See the history
for more details.
Breaking changes
were made to the API
in version 5.0.0.
Specifically,
the predicates isMap and error were removed
in favour of the new predicate builtIn,
which can be used to test for
all built-in objects.
See the history
for more details.
Breaking changes
were made to the API
in version 4.0.0.
Specifically,
the predicate unemptyString
was renamed to nonEmptyString
and the predicate error
was changed to support
derived Error objects.
See the history
for more details.
Breaking changes
were made to the API
in version 3.0.0.
Specifically,
the predicate length
was renamed to hasLength
and the predicate webUrl
was removed.
See the history
for more details.
Breaking changes
were made to the API
in version 2.0.0.
Specifically:
gitUrl, email and floatNumber were removed.verify was renamed to assert.nulled was renamed to null.oddNumber was renamed to odd.evenNumber was renamed to even.positiveNumber was renamed to positive.negativeNumber was renamed to negative.intNumber was renamed to integer.bool was renamed to boolean.defined was swapped to become undefined.webUrl was tightened to reject more cases.See the history
for more details.
Breaking changes
were made to the API
in version 1.0.0.
Specifically,
all of the predicates
were renamed
from check.isXxxx
to check.xxx and
all of the verifiers
were renamed
from check.verifyXxxx
to check.verify.xxx.
See the history
for more details.
The build environment relies on
Node.js,
NPM,
JSHint,
Mocha,
Chai,
UglifyJS and
please-release-me.
Assuming that you already have Node.js and NPM set up,
you just need to run npm install to
install all of the dependencies as listed in package.json.
The unit tests are in test/check-types.js.
You can run them with the command npm test.
To run the tests in a web browser,
open test/check-types.html.