static-props

defines static object attributes using Object.defineProperties

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'

const staticProps = require('static-props')
// Or use ES6: import staticProps from '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.
    const enumerable = true
    staticProps(this)({x, y}, enumerable)
  }
}

// Add a static class attribute.
staticProps(Point2d)({ dim: 2 })

const norm = (x, y) => x * x + y * y
// A particular case are static methods, since they are functions
// they must be wrapped otherwise are considered as getters.
staticProps(Point2d)({ norm: () => norm })

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

const p = new Point2d(1, 2)

// Trying to modify a static prop will throw, as expected.
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 }

You can access static class attributes and methods.

console.log(Point2d.dim) // 2
console.log(Point2d.norm(1, 2)) // 5

Annotated source

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

Add every prop to obj as not writable nor configurable, i.e. static. If prop is a function use it as a getter, otherwise use it as a value. Finally, apply the Object.defineProperties function.

/**
 * @param {Object} obj
 * @returns {Function}
 */
function staticProps (obj) {
  /**
   * @param {Object} props
   * @param {Boolean} [enumerable]
   */
  return function (props, enumerable) {
    var staticProps = {}

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

      var prop = props[propName]

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

        staticProp.writable = false
      }

      staticProps[propName] = staticProp
    }

    Object.defineProperties(obj, staticProps)
  }
}

Export function, supporting both CommonJS and ES6.

module.exports = exports.default = staticProps

License

MIT