Neden

Bare bones Empirical Modelling support for Node.JS, allowing any Javascript value to be established as an observable and Javascript functions to be used to establish a dependency.

Installation

To use neden, add it to your package using npm in the normal way:

npm install --save neden

The package has one function that you require in your code:

var eden = require('neden');

This code is intended to be used in the Node.JS REPL for interactive and iterative experimentation.

Usage

Declare observables

Declare observables as follows:

var a = eden(1);
var b = eden(true);
var c = eden('hello');
var d = eden([1, 2, 3]);

Each declaration returns a function.

Read values

To read the values of observables, call the associated function with no arguments:

a();
# 1
b();
# true
c();
# 'hello'
d();
# [1, 2, 3]

Change observables

To change the value of an observable, call the association function with a single argument containing the replacement value:

a(2);
# 2
b(false);
# false
c(7);
# 7 - note that the observable changes type
d({ key: 'value'});
# { key : 'value' } - also changes type

Do not declare the variables again as this will orphan the observable and not trigger any changes of dependent values.

Create a dependency

Create a new dependency using a function and the observables that it depends upon.

var s = eden((x, y) => x + y, a, c);

Note that you could also do the same assuming with an unbounded argument list:

var t = eden((...x) => x.reduce((y, z) => y + z), a, c);

In both cases, the value returned is a function.

Read the value of an evaluated dependency

To read the value of an evaluated dependency, call the associated function with no arguments:

s();
# 9

Redefine a dependency

Call the associated function with a replacement function and dependencies:

s(x => x - 1, a);
s();
# 1

To break all dependencies, change s into an observable, perhaps setting the value to null:

s(null);

Inspect the dependency tree

Observables and definitions have a property called deps which is an object containing a map from the unique internal identifier of any value that depends on this value and the function to call to update the dependent value.

Definitions have a value called dpnd which is an array of all the observables that are depended on. They also have a value called f which is the function to call to update the values.

These values can be inspected in the REPL by typing the function name without calling the function, for example:

a;
# { [Function: ob]
#   deps: { '0fdacd4d-9257-42c1-889d-a631507d3172': [Function: fn] },
#   dpnd: [],
#   f: undefined }

s;
# { [Function: ob]
#   deps: {},
#   dpnd: [ { [Function: ob] deps: [Object], dpnd: [], fn: undefined } ],
#   f: [Function] }

s.f.toString();
# 'x => x - 1'

Asynchronous behaviour

Neden can be used with Node.JS promises. For example:

var tp = (v, t) => new Promise((f, r) => { setTimeout(() => f(v), t); });
var ta = (...x) => Promise.all(x).then(y => y.reduce((x, y) => x + y));
var a = eden(tp(7, 3000));
var b = eden(tp(42, 8000));
var c = eden(ta, a, b);
c();
# Promise { <pending> }

# Wait 8 seconds
c();
# Promise { 49 }

Status and next steps

This is an experimental prototype for research purposes only with no commitment to further development.