static-props

defines static object attributes using Object.defineProperties

Table Of Contents:

• Installation
• Usage
• Annotated source
• License

Installation

With npm do

npm install static-props --save

Usage

Let's create a classic Point2d class and add constant attributes.

'use strict'

var staticProps = require('static-props')

class Point2d {
  constructor (x, y, label) {
    // Suppose you have few static attributes in your class.
    const color = 'red'

    // Create a getter.
    const norm = () => x * x + y * y

    // Add constant attributes quickly.
    staticProps(this)({label, color, norm})

    // Add enumerable attributes.
    var enumerable = true
    staticProps(this)({x, y}, enumerable)
  }
}

After instantiating the class, we can check that its props cannot be changed.

var p = new Point2d(1, 2)

// Trying to modify a static prop will throw as you expect.
p.label = 'B'
// TypeError: Cannot assign to read only property 'label' of #<Point2d>

Props label and color are values, while norm is a getter.

console.log(p.label) // 'A'
console.log(p.color) // 'red'
console.log(p.norm) // 5 = 1 * 1 + 2 * 2

Attributes x, y were configured to be enumerable

console.log(p) // Point2d { x: 1, y: 2 }

If you want to add a static attribute class, you can also do

staticProps(Point2d)({ dim: 2 })

so you can access it with

console.log(Point2d.dim) // 2

Annotated source

API is staticProps(obj)(props[, enumerable])

/**
 * @param {Object} obj
 * @returns {Function}
 */

function staticProps (obj) {
  /**
   * @param {Object} props
   * @param {Boolean} [enumerable]
   */

  return function (props, enumerable) {

Add every prop to obj as not writable nor configurable, i.e. static

    var staticProps = {}

    for (var propName in props) {
      var staticProp = {
        configurable: false,
        enumerable: enumerable
      }

If prop is a function use it as a getter, otherwise as a value

      var prop = props[propName]

      if (typeof prop === 'function') staticProp.get = prop
      else {
        staticProp.value = prop

        staticProp.writable = false
      }

      staticProps[propName] = staticProp
    }

Finally, apply the Object.defineProperties function

    Object.defineProperties(obj, staticProps)
  }
}

Export function

module.exports = staticProps

License

MIT