checkorator v0.0.1

@checkorator

Checkorator is a library providing a simple decorator system for asserting function parameters.

Usage

Checkorator is designed to be used with typescript decorators.

To assert that a parameter is not null or undefined:

import { check, is, present } from 'checkorator';

@check()
class Foo {
    private bar: string;

    constructor(@is(present) bar: string) {
        this.bar = bar;
    }
}

If we manage to pass in a bad value:

new Foo(undefined as any);

// Assertion Error: Foo: parameter #1 failed check

Reference

Decorators

check(): ClassDecorator

Used to decorate a class. Will run all existing checks when the constructor is called.

e.g.

@check()
class Foo {}

is(fn: (x: any) => boolean): ParameterDecorator

Used to decorator function parameters. Adds the supplied function as a check on the decorated parameter. Can be used with helper functions from this library, or any function that takes one parameter and returns a boolean;

e.g.

constructor(@is(aString) foo: string) {}

or

constructor(@is(x => x === 'this exact string') foo: string) {}

is Helpers

present(x: any): boolean

Fails if the value is null or undefined

e.g.

constructor(@is(present) foo: string) {}

notNull(x: any): boolean

Fails if the value is null (undefined will pass);

e.g.

constructor(@is(notNull) foo: string) {}

notUndefined(x: any): boolean

Fails if the value is undefined (null will pass);

e.g.

constructor(@is(notUndefined) foo: string) {}

aString(x: any): boolean

Passes if the value is typeof 'string'

e.g.

constructor(@is(aString) foo: string) {}

aNumber(x: any): boolean

Passes if the value is typeof 'number'

e.g.

constructor(@is(aNumber) foo: number) {}

anArray(x: any): boolean

Checks the value with Array.isArray

e.g.

constructor(@is(anArray) foo: string[]) {}

Helper Factories

longerThan(n: number): (x: any) => boolean

Passes if the value an array or string longer than n

e.g.

constructor(@is(longerThan(5)) foo: string) {}

shorterThan(n: number): (x: any) => boolean

Passes if the value an array or string shorter than n

e.g.

constructor(@is(shorterThan(5)) foo: number[]) {}

length(n: number): (x: any) => boolean

Passes if the value an array or string with length of exactly n

e.g.

constructor(@is(length(5)) foo: string) {}

Roadmap

Short term feature goals:

1. is should also allow a map of recursively defined checks for asserting deep properties
2. is should preserve parameter names if possible
3. is should allow optionally defining failure output
4. check should allow passing an array of checks or a number-indexed map of checks to augment/replace is
5. Continue to define useful helpers for is when found.