defines static object attributes using Object.defineProperties
npm install static-props> defines static object attributes using Object.defineProperties
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With npm do
``bash`
npm install static-props --save
Let's create a classic Point2d class and add constant attributes.
`js
'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.
`js
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 #
`
Props label and color are values, while norm is a getter.
`js`
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.
`js`
console.log(p) // Point2d { x: 1, y: 2 }
You can access static class attributes and methods.
`js`
console.log(Point2d.dim) // 2
console.log(Point2d.norm(1, 2)) // 5
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.
`javascript
/**
* @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.
`javascript``
module.exports = exports.default = staticProps