lazy-initializer

Lazy Initializer

Lazy Initializer is a generic deferred object initializer, which will creates a wrapper which waits for your first time use, then it will triggers the initialize function you defined. The concept is similar to C#'s Lazy class, but more transparent implementation in ES6.

Usage

Simple usage for wrapping a property in a class:

import { LazyProperty } from 'lazy-initializer'; // or require(...) if your environment does not support import.

class Schrodinger {
  @LazyProperty
  get cat() { return Math.random() > 0.5; }
  // Setter will be called when the value has been assigned first time.
  // Setters can be not defined, but then the property will be read-only.
  set cat(value) {
    console.log(`It is ${value ? 'alive' : 'dead'} now!`);
    assert.strictEqual(value, this.cat);
  }
}

const isAlive = new Schrodinger().cat;

Alternatively, if your transpiler or environment does not support ES6 decorators:

import { LazyProperty } from 'lazy-initializer';

class Schrodinger {
  get cat() { return Math.random() > 0.5; }
}
LazyProperty.transform(Schrodinger, 'cat');

Also, you may manually craete a new lazy property without defining the getter/setter before:

import { LazyProperty } from 'lazy-initializer';

const someObject = {};
LazyProperty.define(someObject, 'somelazyField', () => 'boo!');
// Then, `someObject` has a `somelazyField` now!

// You may batch define more properties like this:
LazyProperty.define(someObject, {
  someOtherLazyField: () => 'another one!',
  someMoreComplicatedLazyField: {
    init: () => 'More controllable behaviour!',
    enumerable: false,
    configurable: false,
    writable: true,
  },
});

Another advanced usage is wrapping a whole object (which uses proxy):

import { LazyProxy } from 'lazy-initializer';

const somethingExpensive = LazyProxy.create(() => {
  // Some heavy stuffs...
  return someHeavyObject;
});

// You may treat the object is loosely equals to the initialized object itself.
const someValue = somethingExpensive.someValue();

If the lazy initialized object will be used as constructors:

import { LazyProxy } from 'lazy-initializer';

const SomeHeavyConstructor = LazyProxy.create(() => {
  // Some heavy stuffs...
  return Foo;
}, true);
// The true means this will use as constructor,
// the proxy internals will do some tweaks to make this to be supported.

const someValue = new SomeHeavyConstructor();

For more information, please see docs.

Installation

In your Node.js project path, run:

$ npm install --save lazy-initializer

or yarn

$ yarn add lazy-initializer

Requirements

This module make uses the new ES6 features, especially proxy, therefore it requires at least Node.js 6+ to works.

ECMAScript 6 compatibility table

License

MIT