reactive-property

ReactiveProperty

This tiny library abstracts the getter-setter pattern described in Towards Reusable Charts (by Mike Bostock, 2012).

It also adds the ability to react to changes in state.

Quick Start

Install the library by running the command

npm install reactive-property

Require it in your code like this:

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

Create your first property.

var a = ReactiveProperty();

Set its value.

a(5);

Get its value.

a();

Listen for changes.

a.on(function(){
  console.log("The value of 'a' changed!");
});

Cancel your subscription.

var listener = a.on(function(){
  console.log("The value of 'a' changed!");
});
a.off(listener);

Example Code

Here's some example code from the tests that demonstrates the functionality of this library.

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

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

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

  it("Should set 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.

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 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);
});

Here's how you can unregister a listener.

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);
});

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