@kavi4/measure-units v1.1.2

measure-units

Solution for converting you measure units

Features

• no dependencies
• can support different numeric libraries (bignumber.js and so on)
• convert measure units
• can convert to prefer unit (smallest unit with a value greater than 1)

Install

npm i @kavi4/measure-units

Usage

For each measure unit group we should define dictionary of codes, then define coefficient map and create converter

Dictionary with measure unit codes

Its can be just object with constants:

// units.js
export default {
    GRAM: 'g',
    KILOGRAM: 'kg',
    TON: 'ton',
}

Coefficient map

Coefficient map define measure units relation. All coefficients should be sorted (desc). Set base unit (Units.GRAM) and write coefficients relatively base unit:

//coefficients.js
import {CoefficientMap} from 'masure-units'
import Units from './units'

export default new CoefficientMap([
    [Units.TON, 1000000],
    [Units.KILOGRAM, 1000],
    [Units.GRAM, 1],
])

If you are using third party coefficient map you can include only units than you are using with help include and exclude methods:

import {Units, MassCoefficientMap} from 'some-package'

const map = new MassCoefficientMap()

//includes only this units
map.include([
    Units.KILOGRAM,
    Units.GRAM,
    Units.MILLIGRAM
])

map.exclude([
      Units.GRAM,
])

// result map contains  Units.KILOGRAM and Units.MILLIGRAM

If you are using numeric library you can transform coefficients with method map:

import coefficients from './coefficients'

coefficients =  coefficients.map((value,key,map)=>{
    return new BigNumber(value)
})

Create math instance

We use math class because javascript have't normal support operator overloading.

Math used for arithmetic operations in measure unit converters. From box you have NativeMath:

 import {NativeMath} from 'measure-units'
 
 let math = new NativeMath()

You can implement self math class with IMath, for example:

// bigNumberMath.js
import {IMath} from 'measure-units'

class BigNumberMath extends IMath {
   abs(value) {
       return value.abs()
   }

   multiplication(a, b) {
       return a.multipliedBy(b)
   }

   division(a, b) {
       return a.dividedBy(b)
   }

   greaterOrEqual(a, b) {
       return a.gte(b)
   }
}

Create MeasureUnitConverter

MeasureUnitConverter used for converting units from group

import {MeasureUnitConverter} from 'measure-units'
import coefficients from './coefficients'
import BigNumberMath from './bigNumberMath'

const massConverter = new MeasureUnitConverter({
    coefficientMap:coefficients,
    math: new BigNumberMath(),
})

Then we can join all our converters in one facade. MeasureUnitFacade implements IMeasureUnitConverter and we can use facade as converter

import {MeasureUnitFacade} from 'measure-units'
import Units from './units'

const Unit = new MeasureUnitFacade([
    massConverter,
    volumeConverter,
    lengthConverter,
])

Unit.convert(5, Units.GRAM, Units.KILOGRAM)
// 0.005

Unit.convertToPreferUnit(5000, Units.GRAM)
// {value: 5, unit: 'kg'}

If we store measure unit values in objects we can write adapter. For example :

class ConverterAdapter {
    
    constructor(converter){
        this.converter = converter
    }
    /**
    * @param Unit unit // {value:1, code:'kg'}
    * @param destinationUnit
    */
    convert(unit,destinationUnit){
        let result = new Unit()
        result.value = this.converter.convert(unit.value, unit.code, destinationUnit)
        result.code = destinationUnit
        
        return result
    }
}