dynamic-context

Dynamic context manages your mutation stack allowing your application to easily share context in an idempotent way.

What does that actually mean?

When you change an individual value, an entirely new context is created - all of the original values are copied forward and only the new value is actually changed.

> npm install -S dynamic-context

const _context = require('dynamic-context');

const homer = _context(['firstName', 'lastName']).lastName('Simpson').firstName('Homer');
const marge = homer.firstname('Marge');

console.log(`${homer.firstName()} ${homer.lastName()}`);
// Homer Simpson
console.log(`${marge.firstName()} ${marge.lastName()}`);
// Marge Simpson

Values can also be changed via a setter, which allows you to clear a value that you've previously defined.

const _context = require('dynamic-context');

const homer = _context(['firstName', 'lastName']).lastName('Simpson').firstName('Homer');
const marge = homer.set('firstName', 'Marge');
const unknown = homer.set('firstName');

console.log(`${homer.firstName()} ${homer.lastName()}`);
// Homer Simpson
console.log(`${marge.firstName()} ${marge.lastName()}`);
// Marge Simpson
console.log(`${unknown.firstName()} ${unknown.lastName()}`);
// undefined Simpson

You can also access the parent context which allows you to traverse up the context tree.

const _context = require('dynamic-context');

const homer = _context(['firstName', 'lastName', 'relation']).lastName('Simpson').firstName('Homer');
const bart = homer.relation('son').firstName('Bart');
const lisa = homer.relation('daughter').firstName('Lisa');

console.log(`${bart.firstName()} ${bart.lastName()} ${bart.relation()} of ${bart.parent().firstName()}`);
// Bart Simpson son of Homer
console.log(`${lisa.firstName()} ${lisa.lastName()} ${lisa.relation()} of ${lisa.parent().firstName()}`);
// Lisa Simpson daughter of Homer

Whilst individual values are idempotent, they are subject to the same variability as all other javascript objects.

const _context = require('dynamic-context');

const obj = {
  firstName: 'Homer',
  lastName: 'Simpson'
}

const homer = _context(['person']).person(obj);
obj.firstName = 'Marge';

console.log(`${homer.person().firstName} ${homer.person().lastName}`);
// Marge Simpson <<-- notice that the name may not be what you expected