@citybrewcoffee/rule-engine v1.1.1

Tyepscript Rule Engine

This package is meant to help with processing complex rules and checking if dynamic data fits those rules.

Quickstart

You can start by creating your own rule by extending the rule object and implement an isValid() function. Here's an example:

class StringContainsRule extends Rule<string> {
  type = 'STRING_CONTAINS_RULE';

  letterToContain: string;

  constructor(letterToContain: string) {
    super();
    this.letterToContain = letterToContain;
  }

  isValid(input: string): boolean {
    return input.includes(this.letterToContain);
  }
}

Built in Rules

There are 3 rules already made by this package that can be used out of the box:

• Rule Group: Takes in a list of rules as subrules; isValid() return the logical 'AND' or 'OR' of the rules
• Not Rule: Takes in a rule; isValid() return the logical NOT of the rule
• List Rule: Takes in a rule of specific type and optional parameters on how to calculate the end result; isValid() takes a list of objects and returns true if conditions are met on the list (ie all items meet certain rule, or exacly 5 items, ect)

Serializing

All rules inherit a toJson() method and toObject() method for storage in a database.

Deserializing with Rule Store

A RuleStore is an object in memory that knows how to build rules from json or plain objects. RuleStores already know how to build built-in rules (RuleGroup, ListRule, and NotRule), and you can "teach" it how to build your custom rules by feeding it a type string and build function, like so:

const store = new RuleStore([
  {
    type: 'STRING_CONTAINS_RULE',
    build: (json) => new StringContainsRule(json.letterToContain as string),
  },
]);

Rule Return Type

While rules will return boolean by default, you can add a second optional generics paramters to rules to make them return something else, like a number. Here's an example.

class StringLengthRule extends Rule<string, number> {
  type = 'STRING_LENGTH_RULE';
  isValid(input: string): number {
    return input.length;
  }
}

Note that if your rule doesn't return booleans, it can not be used with the built-in RuleGroup, NotRule, or ListRule.