reactive-property

ReactiveProperty

A simple library that generates getter-setters.

This abstracts the getter-setter pattern described in Towards Reusable Charts - Mike Bostock (2012);

Here are the tests that demonstrate the functionality of this library:

var ReactiveProperty = require("reactive-property");
var assert = require("assert");

describe("Getter-setters", function() {

  it("Should construct a property.", function () {
    var a = ReactiveProperty();
    assert.equal(typeof(a), "function");
    assert.equal(typeof(a()), "undefined");
  });

  it("Should construct a property with a default value and get the value.", function () {
    var a = ReactiveProperty(5);
    assert.equal(a(), 5);
  });

  it("Should set and the value.", function () {
    var a = ReactiveProperty();
    a(10);
    assert.equal(a(), 10);
  });

  it("Should set and the value, overriding the default value.", function () {
    var a = ReactiveProperty(5);
    a(10);
    assert.equal(a(), 10);
  });

});

In addition to setting and getting values, you can also listen for changes using the on function.

describe("Reacting to changes", function (){

  it("Should react to changes.", function (done) {
    var a = ReactiveProperty();
    a.on(function (){
      assert.equal(a(), 10);
      done();
    }); 
    a(10);
  });

  it("Should react to the default value.", function (done) {
    var a = ReactiveProperty(5);
    a.on(function (){
      assert.equal(a(), 5);
      done();
    }); 
  });

  it("Should not react to no value.", function () {
    var a = ReactiveProperty();
    var numInvocations = 0;
    a.on(function (){ numInvocations++; }); 
    assert.equal(numInvocations, 0);
  });

  it("Should react synchronously.", function () {
    var a = ReactiveProperty();
    var numInvocations = 0;
    a.on(function (){ numInvocations++; }); 
    assert.equal(numInvocations, 0);
    a(10);
    assert.equal(numInvocations, 1);
    a(15);
    assert.equal(numInvocations, 2);
  });

  it("Should stop reacting to changes.", function () {
    var a = ReactiveProperty();
    var numInvocations = 0;
    var listener = a.on(function (){ numInvocations++; }); 
    a(10);
    assert.equal(numInvocations, 1);
    a.off(listener);
    a(15);
    assert.equal(numInvocations, 1);
  });

  it("Should pass the value to the listener as an argument.", function (done) {
    var a = ReactiveProperty();
    a.on(function (value){
      assert.equal(value, 10);
      done();
    }); 
    a(10);
  });
});

I hope you enjoy this library! Feel free to open GitHub issues if you have any questions, comments or suggestions.