spec-pattern

Implementation of the Specification Pattern for JavaScript and TypeScript.

Build complex filters and rules easily.

• No external dependencies;
• Fully tested;
• Semantic versioning;
• Forks are welcome! See how to contribute.

Installation

$ npm i spec-pattern

Usage

Without syntax sugar

A simple Between rule

import { Between } from 'spec-pattern';

const rating = new Between( 1, 5 );

console.log( rating.isSatisfiedBy( 3 ) ); // true
console.log( rating.isSatisfiedBy( 0 ) ); // false

A little more complex Between rule

import { Between } from 'spec-pattern';

const desiredAgesToAnswerSurvey = new Between( 16, 21 )
	.or( new Between( 65, 120 ) );

console.log( desiredAgesToAnswerSurvey.isSatisfiedBy( 18 ) ); // true
console.log( desiredAgesToAnswerSurvey.isSatisfiedBy( 70 ) ); // true
console.log( desiredAgesToAnswerSurvey.isSatisfiedBy( 5 ) ); // false

Composing rules

import { Between, In, GreaterThan } from 'spec-pattern';

const someCrazyRule = new Between( 1, 3 )
   .or( new Between( 6, 9 ) )
   .or( new In( [ 11, 25, 31 ] ) )
   .or( new GreaterThan( 50 ) );

console.log( someCrazyRule.isSatisfiedBy( 2 ) ); // true
console.log( someCrazyRule.isSatisfiedBy( 7 ) ); // true
console.log( someCrazyRule.isSatisfiedBy( 5 ) ); // false
console.log( someCrazyRule.isSatisfiedBy( 11 ) ); // true
console.log( someCrazyRule.isSatisfiedBy( 50 ) ); // false
console.log( someCrazyRule.isSatisfiedBy( 51 ) ); // true

// Printable !
console.log( someCrazyRule.toString() );
// (((between (1, 3) or between (6, 9)) or in [11, 25, 31]) or greater than 50)

Not only numbers

import { StartsWith, Contains } from 'spec-pattern';

const helloWithoutWorld = new StartsWith( 'Hello' )
    .andNot( new Contains( 'world' ) );

console.log( helloWithoutWorld.isSatisfiedBy( 'Hello Bob' ) ); // true
console.log( helloWithoutWorld.isSatisfiedBy( 'Hello world' ) ); // false

import { LengthBetween, EqualTo } from 'spec-pattern';

const crazyText = new LengthBetween( 2, 5 )
    .andNot( new EqualTo( 'Hello' ) );

console.log( crazyText.isSatisfiedBy( '' ) ); // false
console.log( crazyText.isSatisfiedBy( 'Hi' ) ); // true
console.log( crazyText.isSatisfiedBy( 'Hello' ) ); // false
console.log( crazyText.isSatisfiedBy( 'Howdy' ) ); // true
console.log( crazyText.isSatisfiedBy( 'Hello world' ) ); // false

With syntax sugar

A simple Between rule

import { between } from 'spec-pattern';

const rating = between( 1, 5 );

console.log( rating.isSatisfiedBy( 3 ) ); // true
console.log( rating.isSatisfiedBy( 0 ) ); // false

A little more complex Between rule

import { between } from 'spec-pattern';

const desiredAgesToAnswerSurvey = between( 16, 21 )
	.or( between( 65, 120 ) );

console.log( desiredAgesToAnswerSurvey.isSatisfiedBy( 18 ) ); // true
console.log( desiredAgesToAnswerSurvey.isSatisfiedBy( 70 ) ); // true
console.log( desiredAgesToAnswerSurvey.isSatisfiedBy( 5 ) ); // false

Composing rules

import { between, isIn, greaterThan } from 'spec-pattern';

const someCrazyRule = between( 1, 3 )
   .or( between( 6, 9 ) )
   .or( isIn( [ 11, 25, 31 ] ) )
   .or( greaterThan( 50 ) );

console.log( someCrazyRule.isSatisfiedBy( 2 ) ); // true
console.log( someCrazyRule.isSatisfiedBy( 7 ) ); // true
console.log( someCrazyRule.isSatisfiedBy( 5 ) ); // false
console.log( someCrazyRule.isSatisfiedBy( 11 ) ); // true
console.log( someCrazyRule.isSatisfiedBy( 50 ) ); // false
console.log( someCrazyRule.isSatisfiedBy( 51 ) ); // true

// Printable !
console.log( someCrazyRule.toString() );
// (((between (1, 3) or between (6, 9)) or in [11, 25, 31]) or greater than 50)

Not only numbers

import { startsWith, contains } from 'spec-pattern';

const helloWithoutWorld = startsWith( 'Hello' )
    .andNot( contains( 'world' ) );

console.log( helloWithoutWorld.isSatisfiedBy( 'Hello Bob' ) ); // true
console.log( helloWithoutWorld.isSatisfiedBy( 'Hello world' ) ); // false

import { lengthBetween, equalTo } from 'spec-pattern';

const crazyText = lengthBetween( 2, 5 )
    .andNot( equalTo( 'Hello' ) );

console.log( crazyText.isSatisfiedBy( '' ) ); // false
console.log( crazyText.isSatisfiedBy( 'Hi' ) ); // true
console.log( crazyText.isSatisfiedBy( 'Hello' ) ); // false
console.log( crazyText.isSatisfiedBy( 'Howdy' ) ); // true
console.log( crazyText.isSatisfiedBy( 'Hello world' ) ); // false

Available sugar

There is a corresponding sugar function for every available class. Sugar functions are always named in camelCase. For instance, sameValueAs() for the class SameValueAs. The only exception is the class In. Since in is a reserved word in JavaScript and thus cannot be a function name, the corresponding sugar is isIn.

Available classes

• SameValueAs( value: any ): equality of values, not of types, not of instances
• StrictSameValueAs( value: any ): equality of values and types, not of instances
• EqualTo( value: any ): equality of values or instances, with ==
• StrictEqualTo( value: any ): equality of values and types or of instances, with ===
• SameTypeAs( value: any ): equality of types
• GreaterThan( value: any )
• GreaterThanOrEqualTo( value: any )
• LessThan( value: any )
• LessThanOrEqualTo( value: any )
• Between( min: any, max: any )
• In( values: array ): inside an array
• StartsWith( value: string, ignoreCase: boolean = false ): string starts with
• EndsWith( value: string, ignoreCase: boolean = false ): string ends with
• Contains( value: string, ignoreCase: boolean = false ): string contains
• LengthBetween( min: any, max: any ): string length between two values
• Empty(): string is empty or array is empty
• Matches( regex: RegExp ): matches a regular expression
• Any( ...specs: Spec ): composite that takes in multiple Specs and performs an or
• All( ...specs: Spec ): composite that takes in multiple Specs and performs an and

All these classes extend the abstract class Composite, which in turn implements the interface Spec:

export interface Spec< C, T extends C | unknown > {

    isSatisfiedBy( candidate: C | T ): boolean;

    and( other: Spec< C, T > ): Spec< C, T >;

    andNot( other: Spec< C, T > ): Spec< C, T >;

    or( other: Spec< C, T > ): Spec< C, T >;

    orNot( other: Spec< C, T > ): Spec< C, T >;

    xor( other: Spec< C, T > ): Spec< C, T >;

    xorNot( other: Spec< C, T > ): Spec< C, T >;

    not(): Spec< C, T >;

}

Creating your own class

Create your own class by extending the abstract class Composite, like in the following example. Of course, you can also extend one of the aforementioned classes or implement the interface Spec (but why reinventing the wheel, right?).

Let's create a class DifferentFrom ...

...in TypeScript:

import { Composite } from 'spec-pattern';

export class DifferentFrom< C, T extends C | unknown > extends Composite< C, T > {

    constructor( private _value: T ) {
        super();
    }

    isSatisfiedBy( candidate: C | T ): boolean {
        return this._value != candidate;
    }

    toString(): string {
        return 'different from ' + this._value;
    }

}

...or in JavaScript 6+:

import { Composite } from 'spec-pattern';

class DifferentFrom extends Composite {

    constructor( value ) {
        this.value = value;
    }

    isSatisfiedBy( candidate ) {
        return this.value != candidate;
    }

    toString() {
        return 'different from ' + this.value;
    }
}

...or in JavaScript 5+:

var Composite  = require( 'spec-pattern' ).Composite;

function DifferentFrom( value ) {

    Composite.call( this ); // super()

    this.value = value;

    this.isSatisfiedBy = function ( candidate ) {
        return this.value != candidate;
    };

    this.toString = function() {
        return 'different from ' + this.value;
    };
}

DifferentFrom.prototype = Object.create( Composite.prototype );
DifferentFrom.prototype.constructor = DifferentFrom;

That's it! Just three methods: constructor, isSatisfiedBy, and toString().

License

MIT © Thiago Delgado Pinto