Natural Pleistocene Monsters


    7.5.5 • Public • Published


    bower version npm version npm downloads Build Status Code Coverage Gitter

    If that build is ever red or the coverage is ever less than 100% then I want you to flame me on twitter (@kentcdodds) and be sure to mention how disappointed @josepheames would be in me

    It's like ReactJS propTypes without React. Actually, it's very heavily inspired by this concept. It's purpose is for normal JavaScript functions rather than just React Components.

    Demo Screenshot


    $ npm i -S api-check or $bower i -S api-check

    api-check utilizes UMD, so you can:

    var apiCheck = require('api-check')(/* your custom options, checkers*/);

    Also available as an AMD module or as apiCheck on global


    Note, there are a bunch of tests. Those should be instructive as well.

    var myApiCheck = require('api-check')({
      /* config options */
      output: {
        prefix: 'app/lib Name',
        suffix: 'Good luck!',
        docsBaseUrl: ''
      verbose: false
    }, {
      /* custom checkers if you wanna */
    // given we have a function like this:
    function foo(bar, foobar) {
      // we can define our api as the first argument to myApiCheck.warn
      myApiCheck.warn([myApiCheck.number, myApiCheck.arrayOf(myApiCheck.string)], arguments);
      // do stuff
    // the function above can be called like so:
    foo(3, ['a','b','c']);
    // if it were called like so, a descriptive warning would be logged to the console
    foo('whatever', false);
    // here's something a little more complex (this is what's in the screenshot and [the demo](,console,output))
    var myCheck = require('api-check')({
      output: {
        prefix: 'myApp',
        suffix: 'see docs -->',
        docsBaseUrl: ''
    function doSomething(person, options, callback) {
      myCheck.warn([ // you can also do myCheck.throw to throw an exception
          name: myCheck.shape({
            first: myCheck.string,
            last: myCheck.string
          age: myCheck.number,
          isOld: myCheck.bool,
          walk: myCheck.func,
          ipAddress: function(val, name, location) {
            if (!/(\d{1,3}\.){3}\d{1,3}/.test(val)) {
              return myCheck.utils.getError(name, location, 'ipAddress');
          childrenNames: myCheck.arrayOf(myCheck.string).optional
      ], arguments, {
        prefix: 'doSomething',
        suffix: 'Good luck!',
        urlSuffix: 'dosomething-api-check-failure'
      // do stuff
    var person = {
      name: {
        first: 'Matt',
        last: 'Meese'
      age: 27,
      isOld: false,
      ipAddress: '',
      walk: function() {}
    function callback() {}
    var options = 'whatever I want because it is an "any" type';
    console.log('Successful call');
    doSomething(person, options, callback);
    console.log('Successful call (without options)');
    doSomething(person, callback); // <-- options is optional
    console.log('Failed call (without person)');
    doSomething(callback); // <-- this would fail because person is not optional
    person.ipAddress = 'Invalid IP Address!!!';
    console.log('Failed call (invalid ip address)');
    doSomething(person, options, callback); // <-- this would fail because the ipAddress checker would fail
    // if you only wish to check the first argument to a function, you don't need to supply an array.
    var libCheck = apiCheck(); // you don't HAVE to pass anything if you don't want to.
    function bar(a) {
      var errorMessage = libCheck(apiCheck.string, arguments);
      if (!errorMessage) {
        // success
      } else if (typeof errorMessage === 'string') {
        // there was a problem and errorMessage would like to tell you about it
    bar('hello!'); // <-- success!

    Differences from React's propTypes

    Differences in Supported Types noted below with a *

    • All types are required by default, to set something as optional, append .optional
    • checkApi.js does not support element and node types
    • checkApi.js supports a few additional types
    • object fails on null. Use object.nullOk if you don't want that

    Similarities to React's propTypes

    This project was totally written from scratch, but it (should) support the same api as React's propTypes (with the noted difference above). If you notice something that functions differently, please file an issue.

    apiCheck(), apiCheck.warn(), and apiCheck.throw()

    These functions do the same thing, with minor differences. In both the warn and throw case, a message is generated based on the arguments that the function was received and the api that was defined to describe what was wrong with the invocation.

    In all cases, an object is returned with the following properties:

    argTypes (arrayOf[Object])

    This is an array of objects representing the types of the arguments passed.

    apiTypes (arrayOf[Object])

    This is an object representing the types of the api. It's a whole language of its own that you'll hopefully get after looking at it for a while.

    failed (boolean)

    Will be false when the check passes, and true when it fails

    passed (boolean)

    Will be true when the check passes, and false when it fails

    message (string)

    If the check failed, this will be a useful message for display to the user. If it passed, this will be an empty string

    Also note that if you only have one argument, then the first argument to the apiCheck function can simply be the checker function. For example:

    apiCheck(apiCheck.bool, arguments);

    The second argument can either be an arguments-like object or an array.

    Supported types


    apiCheck.array([]); // <-- pass
    apiCheck.array(23); // <-- fail


    apiCheck.bool(false); // <-- pass
    apiCheck.bool('me bool too?'); // <-- fail


    apiCheck.func(function() {}); // <-- pass
    apiCheck.func(new RegExp()); // <-- fail

    func.withProperties *

    Not available in React's propTypes

    var checker = apiCheck.func.withProperties({
      type: apiCheck.oneOfType([apiCheck.object, apiCheck.string]),
      help: apiCheck.string.optional
    function winning(){}
    winning.type = 'awesomeness';
    checker(winning); // <--pass
    function losing(){}
    checker(losing); // <-- fail


    apiCheck.number(423.32); // <-- pass
    apiCheck.number({}); // <-- fail

    object *

    null fails, use object.nullOk to allow null to pass

    apiCheck.object({}); // <-- pass
    apiCheck.object([]); // <-- fail
    apiCheck.object(null); // <-- fail

    object.nullOk *

    Not available in React's propTypes

    apiCheck.object.nullOk({}); // <-- pass
    apiCheck.object.nullOk([]); // <--- false
    apiCheck.object.nullOk(null); // <-- pass


    apiCheck.string('I am a string!'); // <-- pass
    apiCheck.string([]); // <-- fail


    apiCheck.range(0, 10)(4); // <-- pass
    apiCheck.rang(-100, 100)(500); // <-- fail


    apiCheck.greaterThan(100)(200); // <-- pass
    apiCheck.greaterThan(-10)(-20); // <-- fail
    apiCheck.greaterThan(50)('Frogs!'); // <-- fail


    apiCheck.lessThan(100)(50); // <-- pass
    apiCheck.lessThan(-10)(0); // <-- fail
    apiCheck.lessThan(50)('Frogs!'); // <-- fail


    apiCheck.instanceOf(RegExp)(new RegExp); // <-- pass
    apiCheck.instanceOf(Date)('wanna go on a date?'); // <-- fail


    apiCheck.oneOf(['Treek', ' Wicket Wystri Warrick'])('Treek'); // <-- pass
    apiCheck.oneOf(['Chewbacca', 'Snoova'])('Snoova'); // <-- fail


    apiCheck.oneOfType([apiCheck.string, apiCheck.object])({}); // <-- pass
    apiCheck.oneOfType([apiCheck.array, apiCheck.bool])('Kess'); // <-- fail


    apiCheck.arrayOf(apiCheck.string)(['Huraga', 'Japar', 'Kahless']); // <-- pass
    )([[[1,2,3], [4,5,6], [7,8,9]], [[1,2,3], [4,5,6], [7,8,9]]]); // <-- pass (for realz)
    apiCheck.arrayOf(apiCheck.bool)(['a', 'b', 'c']); // <-- fail

    typeOrArrayOf *

    Not available in React's propTypes

    Convenience checker that combines oneOfType with arrayOf and whatever you specify. So you could take this:

      apiCheck.string, apiCheck.arrayOf(apiCheck.string)



    which is a common enough use case to justify the checker.

    apiCheck.typeOrArrayOf(apiCheck.string)('string'); // <-- pass
    apiCheck.typeOrArrayOf(apiCheck.string)(['array', 'of strings']); // <-- pass
    apiCheck.typeOrArrayOf(apiCheck.bool)(['array', false]); // <-- fail
    apiCheck.typeOrArrayOf(apiCheck.object)(32); // <-- fail


    apiCheck.objectOf(apiCheck.arrayOf(apiCheck.bool))({a: [true, false], b: [false, true]}); // <-- pass
    apiCheck.objectOf(apiCheck.number)({a: 'not a number?', b: 'yeah, me neither (◞‸◟;)'}); // <-- fail

    shape *

    Note: React propTypes does support shape, however it does not support the strict option

    If you add .strict to the shape, then it will enforce that the given object does not have any extra properties outside those specified in the shape. See below for an example...

      name: checkers.shape({
        first: checkers.string,
        last: checkers.string
      age: checkers.number,
      isOld: checkers.bool,
      walk: checkers.func,
      childrenNames: checkers.arrayOf(checkers.string)
      name: {
        first: 'Matt',
        last: 'Meese'
      age: 27,
      isOld: false,
      walk: function() {},
      childrenNames: []
    }); // <-- pass
      mint: checkers.bool,
      chocolate: checkers.bool
    })({mint: true}); // <-- fail

    Example of strict

    var strictShape = apiCheck.shape({
      cookies: apiCheck.bool,
      milk: apiCheck.bool,
      popcorn: apiCheck.bool.optional
    }).strict; // <-- that!
      cookies: true,
      milk: true,
      popcorn: true,
      candy: true
    }); // <-- fail because the extra `candy` property
      cookies: true,
      milk: true
    }); // <-- pass because it has no extra properties and `popcorn` is optional

    Note, you can also append .optional to the .strict (as in: apiCheck.shape({}).strict.optional)

    shape.onlyIf *

    Not available in React's propTypes

    This can only be used in combination with shape

      cookies: apiCheck.shape.onlyIf(['mint', 'chips'], apiCheck.bool)
    })({cookies: true, mint: true, chips: true}); // <-- pass
      cookies: apiCheck.shape.onlyIf(['mint', 'chips'], apiCheck.bool)
    })({chips: true}); // <-- pass (cookies not specified)
      cookies: apiCheck.shape.onlyIf('mint', apiCheck.bool)
    })({cookies: true}); // <-- fail

    shape.ifNot *

    Not available in React's propTypes

    This can only be used in combination with shape

      cookies: apiCheck.shape.ifNot('mint', apiCheck.bool)
    })({cookies: true}); // <-- pass
      cookies: apiCheck.shape.ifNot(['mint', 'chips'], apiCheck.bool)
    })({cookies: true, chips: true}); // <-- fail

    requiredIfNot *

    Not available in React's propTypes

    This can only be used in combination with shape

    checker = checkers.shape({
      foobar: checkers.shape.requiredIfNot(['foobaz', 'baz'], checkers.bool),
      foobaz: checkers.object.optional,
      baz: checkers.string.optional,
      foo: checkers.string.optional
      foo: [1, 2],
      foobar: true
    }); // <-- passes
    checker({foo: 'bar'}); // <-- fails

    Not available in React's propTypes

    This can only be used in combination with shape.requiredIfNot

    checker = checkers.shape({
      foobar: checkers.shape.requiredIfNot.all(['foobaz', 'baz'], checkers.bool),
      foobaz: checkers.object.optional,
      baz: checkers.string.optional,
      foo: checkers.string.optional
      foo: [1, 2]
    }); // <-- fails
      foo: [1, 2],
      foobar: true
    }); // <-- passes
      foo: [1, 2],
      baz: 'foo'
    }); // <-- passes

    args *

    Not available in React's propTypes

    This will check if the given item is an arguments-like object (non-array object that has a length property)

    function foo(bar) {
      apiCheck.args(arguments); // <-- pass
    apiCheck.args([]); // <-- fail
    apiCheck.args({}); // <-- fail
    apiCheck.args({length: 3}); // <-- pass
    apiCheck.args({length: 'not-number'}); // <-- fail


    apiCheck.any({}); // <-- pass
    apiCheck.any([]); // <-- pass
    apiCheck.any(true); // <-- pass
    apiCheck.any(false); // <-- pass
    apiCheck.any(/* seriously, anything, except undefined */); // <-- fail
    apiCheck.any.optional(/* unless you specify optional :-) */); // <-- pass
    apiCheck.any(3); // <-- pass
    apiCheck.any(3.1); // <-- pass
    apiCheck.any(3.14); // <-- pass
    apiCheck.any(3.141); // <-- pass
    apiCheck.any(3.1415); // <-- pass
    apiCheck.any(3.14159); // <-- pass
    apiCheck.any(3.141592); // <-- pass
    apiCheck.any(3.1415926); // <-- pass
    apiCheck.any(3.14159265); // <-- pass
    apiCheck.any(3.141592653); // <-- pass
    apiCheck.any(3.1415926535); // <-- pass
    apiCheck.any(3.14159265359); // <-- pass
    apiCheck.any(jfio,.jgo); // <-- Syntax error.... ಠ_ಠ

    Custom Types

    You can specify your own type. You do so like so:

    var myCheck = require('api-check')({
      output: {prefix: 'myCheck'}
    function ipAddressChecker(val, name, location) {
      if (!/(\d{1,3}\.){3}\d{1,3}/.test(val)) {
        return apiCheck.utils.getError(name, location, ipAddressChecker.type);
    ipAddressChecker.type = 'ipAddressString';
    function foo(string, ipAddress) {
      ], arguments);

    Then, if you invoked that function like this:

    foo('hello', 'not-an-ip-address');

    It would result in a warning like this:

    myCheck apiCheck failed! `Argument 1` passed, `value` at `Argument 2` must be `ipAddressString`
    You passed:
    With the types:
    The API calls for:

    There's actually quite a bit of cool stuff you can do with custom types checkers. If you want to know what they are, look at the tests or file an issue for me to go document them. :-)


    When writing custom types, you may find the utils helpful. Please file an issue to ask me to improve documentation for what's available. For now, check out api-check-utils.test.js


    Note, obviously, these things are specific to apiCheck and not part of React propTypes

    When you create your instance of apiCheck, you can configure it with different options as part of the first argument.


    You can specify some extra options for the output of the message.

    var myApiCheck = require('api-check')({
      output: {
        prefix: 'Global prefix',
        suffix: 'global suffix',
        docsBaseUrl: ''
      verbose: false, // <-- defaults to false
      disabled: false // <-- defaults to false, set this to true in production

    You can also specify an output object to each apiCheck(), apiCheck.throw(), and apiCheck.warn() request:

    myApiCheck(apiCheck.bool, arguments, {
      prefix: 'instance prefix:',
      suffix: 'instance suffix',
      urlSuffix: 'example-error-additional-info'

    A failure with the above configuration would yield something like this:

    Global prefix instance prefix {{error message}} instance suffix global suffix

    As an alternative to urlSuffix, you can also specify a url:

    myApiCheck(apiCheck.bool, arguments, {
      url: ''


    This is the method that apiCheck uses to get the message it throws or console.warns. If you don't like it, feel free to make a better one by simply: apiCheck.getErrorMessage = function(api, args, output) {/* return message */}


    This is the method that apiCheck uses to throw or warn the message. If you prefer to do your own thing, that's cool. Simply apiCheck.handleErrorMessage = function(message, shouldThrow) { /* throw or warn */ }

    Disable apiCheck

    It's a good idea to disable the apiCheck in production. You can disable your own instance of apiCheck as part of the options, but it's probably just better to disable apiCheck globally. I recommend you do this before you (or any of you dependencies) create an instance of apiCheck. Here's how you would do that:

    var apiCheck = require('api-check');
    apiCheck.globalConfig.disabled = true;


    This library was written by Kent C. Dodds. Again, big credits go to the team working on React for thinking up the api. This library was written from scratch, but I'd be lying if I didn't say that I referenced their functions a time or two.


    npm i api-check

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