reactive-function

A library for managing data flows and changing state.

Using this library, you can declaratively construct complex data dependency graphs. The propagation of changes through these graphs is managed for you using a variant of the topological sort algorithm. This allows you to write simpler code in which each reactive function need only be concerned with its inputs and outputs. You can be confident that the functions will be executed in the correct order when their input values change, and that functions whose input values have not changed will not be executed unnecessarily.

Usage

If you are using NPM, install this package with:

npm install reactive-function

Require it in your code like this:

var ReactiveFunction = require("reactive-function");

This library is designed to work with reactive-property, you'll need that too.

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

Suppose you have two reactive properties to represent someone's first and last name.

var firstName = ReactiveProperty("Jane");
var lastName = ReactiveProperty("Smith");

Suppose you'd like to have another property that represents the full name of the person.

var fullName = ReactiveProperty();

You could set the full name value like this.

fullName(firstName() + " " + lastName());

However, this sets the value of fullName only once, and it does not get updated when firstName or lastName change.

Here's how you can define a reactive function that updates the full name whenever the first name or last name changes.

ReactiveFunction({
  inputs: [firstName, lastName],
  output: fullName,
  callback: function (first, last){
    return first + " " + last;
  }
});

This defines a "reactive function" that will be invoked when its inputs (firstName and lastName) are both defined and whenever either one changes. The function will be invoked on the next tick of the JavaScript event loop after it is defined and after any dependencies change.

To force a synchronous evaluation of all reactive functions whose dependencies have updated, you can call

ReactiveFunction.digest();

Now you can access the computed value of the reactive function by invoking it as a getter.

console.log(fullName()); // Prints "Jane Smith"

For more detailed example code, have a look at the tests.

Related work:

• ReactiveJS
• vogievetsky/DVL
• EmberJS Computed Properties
• AngularJS Digest
• ZJONSSON/clues
• Model.js

Thanks to Mike Bostock and Vadim Ogievetsky for suggesting to have the ability to digest within a single tick of the event loop (the main difference between this project and the original model-js). This idea has inspired the construction of this library, which I hope will provide a solid foundation for complex interactive visualization systems.