rules-when

Simple When Rule Construction

[W I P Initial Feb 18th, 2015]

BizRez When Rules

A simple way to dynamically create when rules - A great example how to use the new Function instead of the 'evil' eval.

Intro

Simplicity is elegance.

What we need is a descriptive way to tag Biz(i)ness Rules and catalog, inventory, usage, and change dynamically. Javascript provides a simple way of dynamically creating functions on the fly.

Prime directives, and ables ...

• Easy to understand the code
• Thin
• Self documenting
• Pattern - not an enforcement
• Crazy fast
• Secure from XXS

Dependencies

• Mocha.js for for test infecting the code (good infection)

A few Use Cases for Usage

• Validations
• Calculations
• Automated business rules - decision engine
• Home security, sprinkler systems, and darn maybe your car...

Benefits

• Repository of rules
• Traceability
• Modify the rule not the code
• Dynamic changeability - conditions change so do the execution
• Easy to understand and modify
• Extensible
• Maintainable
• Reusable
• Chainable
• Micro foot print and scalable

Example Setup

//Example Setup

var when = {

    isPerson: "return object.isPerson === true //Comment",
    hasLicense: "return object.license === true //Comment",
    isPersonAndHasLicense: "return when['isPerson'](object) && when['hasLicense'](object)",
    payTax: "return object.payTax === true",
    doHula: "return when['isPerson'](object) && when['hasLicense'](object) && when['payTax'](object)"

}

var calculate = {

    adder: "return object.a + object.b //Comment",
    calculateTax: "return object.amount * 1.8",
    addTax: "if (when['payTax'](object)) {return calculate['calculateTax'](object)}; return 0",
    mutate: "object.tada = 'hello Moto'; return true"

}

//Describe Decision Table
var decisionTable = {

    calcNumber: [["return when['isPerson'](object)", "return calculate['adder'](object)", "return true"],
        ["return when['isPerson'](object)", "return calculate['calculateTax'](object)", "return true"],
        ["return when['isPerson'](object)", "return calculate['calculateTax'](object)", "return true"]
    ]

}

---

image 1

Notice: functions stored as strings. These strings will be translated via the new Function operation

Translate value into functions

        //Create When Condtion functions

        function loadwhenConditions(when) {

            //Convert key[value] into real functions
            for (var key in when) {
                when[key] = new Function('object', 'when', 'calculate', when[key]);
            }

        }

        //Create Calculation functions
        function loadCalcualtions(calculate) {
            //Convert key[value] into real functions
            for (var key in calculate) {
                calculate[key] = new Function('object', 'when', 'calculate', calculate[key]);

            }
        }

Example Run

rules.loadWhenRules(when);
rules.loadCalcualtions(calculate);
rules.loadDecisionTable(decisionTable);

var person = {isPerson: true, license: true, a: 5, b: 10, amount: 500, payTax: true};

console.log("isPerson:" + rules.when('isPerson', person));
console.log("hasLicense:" + rules.when('hasLicense', person));
console.log("adder:" + rules.calculate('adder', person));
console.log("addTax:" + rules.calculate("addTax", person));
console.log("isPersonAndHasLicense:" + rules.when('isPersonAndHasLicense', person));
rules.calculate('mutate',person);
console.log(person.tada);
console.log("decisiontable result:" + rules.decisionTable('calcNumber', person));
console.log("doHula:" + rules.when('doHula',person));

Mocha Test

mocha ./lib/test