bahmutov / check-types.js

A tiny JavaScript library for checking types and throwing exceptions.

check-types.js

A tiny JavaScript library for checking types and throwing exceptions.

• Why would I want that?
• How tiny is it?
• How do I install it?
• How do I use it?
  • Loading the library
  • Calling the exported functions
    • String functions
    • Number functions
    • Function functions
    • Array functions
    • Date functions
    • Object functions
    • Modifiers
    • Batch operations
    • Some examples
• How do I set up the build environment?
• What license is it released under?

Why would I want that?

Writing explicit conditions in your functions for checking arguments and throwing 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.

How tiny is it?

17.7 kb unminified with comments, 2.9 kb minified, 1 kb minified + gzipped.

How do I install it?

Any of the following will do:

npm install check-types

jam install check-types

bower install check-types

component install philbooth/check-types.js

git clone [e-mail]:philbooth/check-types.js.git

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:

require.config({
    paths: {
        check: 'check-types.js/src/check-types'
    }
});

require([ 'check' ], function (check) {
});

If you are including check-types.js with an HTML <script> tag, or neither of the above environments are detected, check-types.js will just export its 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 two types.

• check.isXxxx(thing): These functions are predicates, returning true or false depending on the type and value of thing.

• check.verifyXxxx(thing, message): These functions call their equivalent isXxxx predicate and throw an Error if the result is false.

Additionally, every exported function is available with a maybe modifier that simply returns true if the value is null or undefined, otherwise it delegates to the original, unmodified function. Calls to these functions look like check.maybe.isXxxx(thing) and check.maybe.verifyXxxx(thing).

Finally, there are also some batch operations that allow you to test maps of many predicates at once. These are implemented by check.map, check.any and check.every.

String functions

• check.isString(thing): Returns true if thing is a string, false otherwise.

• check.verifyString(thing, message): Throws an exception unless thing is a string.

• check.isUnemptyString(thing): Returns true if thing is a non-empty string, false otherwise.

• check.verifyUnemptyString(thing, message): Throws an exception unless thing is a non-empty string.

• check.isLength(thing, length): Returns true if thing has a length property that matches the specified length, false otherwise.

• check.verifyLength(thing, length, message): Throws an exception unless thing has a length property that matches the specified length.

Number functions

• check.isNumber(thing): Returns true if thing is a number, false otherwise. In this case, NaN is not considered to be a number.

• check.verifyNumber(thing, message): Throws an exception unless thing is a number. In this case, NaN is not considered to be a number.

• check.isPositiveNumber(thing): Returns true if thing is a number greater than zero, false otherwise.

• check.verifyPositiveNumber(thing, message): Throws an exception unless thing is a number greater than zero.

• check.isNegativeNumber(thing): Returns true if thing is a number less than zero, false otherwise.

• check.verifyNegativeNumber(thing, message): Throws an exception unless thing is a number less than zero.

• check.isEvenNumber(thing): Returns true if thing is an even number, false otherwise.

• check.verifyEvenNumber(thing, message): Throws an exception unless thing is an even number.

• check.isOddNumber(thing): Returns true if thing is an odd number, false otherwise.

• check.verifyOddNumber(thing, message): Throws an exception unless thing is an odd number.

Function functions

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

• check.verifyFunction(thing, message): Throws an exception unless thing is function.

Array functions

• check.isArray(thing): Returns true if thing is an array, false otherwise.

• check.verifyArray(thing, message): Throws an exception unless thing is an array.

• check.isLength(thing, length): Returns true if thing has a length property that matches the specified length, false otherwise.

• check.verifyLength(thing, length, message): Throws an exception unless thing has a length property that matches the specified length.

Date functions

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

• check.verifyDate(thing, message): Throws an exception unless thing is a date.

Object functions

• check.isObject(thing): Returns true if thing is a non-null, non-array, non-date object, false otherwise.

• check.verifyObject(thing, message): Throws an exception unless thing is a non-null, non-array, non-date object.

• check.isEmptyObject(thing): Returns true if thing is an empty object, false otherwise.

• check.verifyEmptyObject(thing, message): Throws an exception unless thing is an empty object.

• check.isInstance(thing, prototype): Returns true if thing is an instance of prototype, false otherwise.

• check.verifyInstance(thing, prototype, message): Throws an exception unless thing is an instance of prototype.

• check.quacksLike(thing, duck): Tests whether an object 'quacks like a duck'. 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.verifyQuack(thing, duck, message): Throws an exception unless thing has all of the properties of duck.

Modifiers

• check.maybe.isXxxx(...) / check.maybe.verifyXxxx(...): Returns true if thing is null or undefined, otherwise it delegates to the original, unmodified function.

Batch operations

• check.map(things, functions): Maps each predicate from the functions object to the corresponding value from things, returning the hash of results. Similar to quacksLike but using functions instead of values. Supports nested objects.

• check.every(predicateResults): Returns true if all properties of the predicateResults object are true, false otherwise.

• check.any(predicateResults): Returns true is any property of the predicateResults object is true, false otherwise.

Some examples

check.isObject(null);
// Returns false

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

check.verifyQuack({}, { foo: 'bar' }, 'Invalid object');
// Throws new Error('Invalid object')

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

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

check.every(
    check.map({
        foo: 0,
        bar: ''
    }, {
        foo: check.isNumber,
        bar: check.isUnemptyString
    })
);
// Returns false

check.any(
    check.map({
        foo: 0,
        bar: ''
    }, {
        foo: check.isNumber,
        bar: check.isUnemptyString
    })
);
// Returns true

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