The check-types npm package provides a collection of functions for asserting types and values in JavaScript. It is designed to help developers enforce type safety and data integrity in their applications by offering a simple and intuitive API for type checking and validation.

What are check-types's main functionalities?

Primitive Type Checking

This feature allows you to check if a value is of a specific primitive type, such as a number, string, or boolean. The code sample demonstrates how to use the package to verify that a value is a number, a string, and a boolean.

const check = require('check-types');

console.log(check.number(42)); // true
console.log(check.string('hello')); // true
console.log(check.boolean(false)); // true

Object and Array Checking

With this feature, you can check if a value is an array or an object. The code sample shows how to validate that a value is an array and an object.

const check = require('check-types');

console.log(check.array([1, 2, 3])); // true
console.log(check.object({ key: 'value' })); // true

Function and Null Checking

This feature enables you to verify if a value is a function or null. The provided code sample illustrates how to check for a function and a null value.

const check = require('check-types');

console.log(check.function(function() {})); // true
console.log(check.null(null)); // true

Other packages similar to check-types

Readme

Source

check-types.js

A tiny JavaScript library for asserting types and values.

Why would I want that?

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.

How tiny is it?

14 kb unminified with comments, 3.7 kb minified, 1.4 kb minified + gzipped.

How do I install it?

If you're using npm:

npm install check-types --save

Or if you just want the git repo:

git clone git@github.com:philbooth/check-types.js.git

If you're into other package managers, it is also available from Bower, Component and Jam.

How do I use it?

Loading the library

If you are running in Node.js, Browserify or another CommonJS-style environment, you can require check-types.js 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.

Calling the exported functions

Once you have loaded the library in your application, a whole bunch of functions are available to call.

For the most part, the exported functions are broadly split into four types.

check.xxx(thing): These functions are predicates, returning true or false depending on the type and value of thing.
check.not.xxx(thing): The not modifier negates a predicate, returning true if the predicate returns false and false if the predicate returns true.
check.maybe.xxx(thing): The maybe modifier returns true if thing is null or undefined, otherwise it returns the result of the predicate.
check.either.xxx(thing).or.yyy(thang): The either modifier returns true if either predicate is true, it will only return false when both predicates are false.
check.assert.xxx(thing, message): The assert modifier calls the equivalent predicate and throws an Error if the result is false. It can also be applied to the not, maybe and either modifiers using the forms check.assert.not.xxx(thing, message), check.assert.maybe.xxx(thing, message) and check.assert.either.xxx(thing, message).or.yyy(thang).

Additionally, there are some batch operations that allow you to apply predicates across multiple values inside arrays or objects. These are implemented by check.apply, check.map, check.any and check.every.

String functions

check.string(thing): Returns true if thing is a string, false otherwise.
check.unemptyString(thing): Returns true if thing is a non-empty string, false otherwise.
check.webUrl(thing): Returns true if thing seems like an HTTP or HTTPS URL, false otherwise.
check.length(thing, value): Returns true if thing has a length property that equals value, false otherwise. If value is undefined, an exception is thrown.

Number functions

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.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.integer(thing): Returns true if thing is an integer, false otherwise.

Function functions

check.function(thing): Returns true if thing is a function, false otherwise.

Array functions

check.array(thing): Returns true if thing is an array, false otherwise.
check.length(thing, value): Returns true if thing has a length property that equals value, false otherwise. If value is undefined, an exception is thrown.

Date functions

check.date(thing): Returns true if thing is a date, false otherwise.

Object functions

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.instance(thing, prototype): Returns true if thing is an instance of prototype, false otherwise.
check.like(thing, duck): Duck-typing checker. Returns true if thing has all of the properties of duck, false otherwise. If either argument is not an object, an exception is thrown.
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.

Boolean functions

check.boolean(thing): Returns true if thing is a boolean, false otherwise.

Modifiers

check.not.xxx(...): Returns the negation of the predicate.
check.maybe.xxx(...): Returns true if thing is null or undefined, otherwise it propagates the return value from its predicate.
check.either.xxx(...).or.yyy(...): Returns true if either predicate is true. Returns false if both predicates are false.
check.assert.xxx(...): Throws an Error if the predicate returns false. The last argument is an optional message to be set on the Error instance. Also works with the not, maybe and either modifiers.

Batch operations

check.apply(things, predicates): Applies each value from the array of things to the corresponding predicate and returns the array of results. Passing a single predicate instead of an array of them applies all of the values to that predicate.
check.map(things, predicates): Maps each value from the data to the corresponding predicate and returns a results object. Supports nested objects.
check.all(results): Returns true if all the result values are true in an array (returned from apply) or object (returned from map).
check.any(predicateResults): Returns true if any result value is true in an array (returned from apply) or object (returned from map).

Some examples

check.even(3);
// Returns false

check.not.even(3);
// Returns true

check.maybe.even(null);
// Returns true

check.either.even(3).or.odd(3);
// Returns true

check.assert.like({ foo: 'bar' }, { baz: 'qux' }, 'Invalid object');
// Throws new Error('Invalid object')

check.assert.not.like({ foo: 'bar' }, { baz: 'qux' }, 'Invalid object');
// Doesn't throw

check.assert.maybe.like(undefined, { foo: 'bar' }, 'Invalid object');
// Doesn't throw

check.assert.either.unemptyString(error, 'Invalid error').or.instance(error, Error);
// Throws if `error` is not an error string or Error instance

check.apply([ 'foo', 'bar', '' ], check.unemptyString);
// Returns false

check.map({
    foo: 2,
    bar: { baz: 'qux' }
}, {
    foo: check.odd,
    bar: { baz: check.unemptyString }
});
// Returns { foo: false, bar: { baz: true } }

check.all(
    check.map(
        { foo: 0, bar: '' },
        { foo: check.number, bar: check.string }
    );
);
// Returns true

check.any(
    check.apply(
        [ 1, 2, 3, '' ],
        check.string
    )
);
// Returns true

Where can I use it?

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, there is hope! The 1.x versions all support old IE and any future 1.x versions will adhere to that.

See the releases for more information.

What changed from 1.x to 2.x?

Breaking changes were made to the API in version 2.0.0.

Specifically:

Support for ES3 was dropped
The predicates 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.
The assigned predicate and the apply batch operation were added.

See the history for more details.

What changed from 0.x to 1.x?

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.

How do I set up the build environment?

The build environment relies on Node.js, NPM, JSHint, Mocha, Chai and UglifyJS. 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.

What license is it released under?

MIT

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Last updated on 17 Dec 2014

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check-types