ts-quantities

Originally a fork of gentooboontoo/js-quantities rewritten in typescript.

Installing ts-quantities

Node

Install it in your project

npm install --save ts-quantities

Import it !

import { Qty } from 'ts-quantities'

Using ts-quantities

Qty

ts-quantities heavily relies on Qty objects. To create Qty objects, use its constructor using new.

qty = new Qty('23 ft');

Qty constructor accepts strings, numbers and Qty instances as initializing values.

If scalars and their respective units are available programmatically, the two argument signature may be useful:

qty = new Qty(124, 'cm'); // => 1.24 meter

qty = new Qty('1m'); // => 1 meter
qty = new Qty('m'); // =>  1 meter (scalar defaults to 1)

qty = new Qty('1 N*m');
qty = new Qty('1 N m'); // * is optional

qty = new Qty('1 m/s');

qty = new Qty('1 m^2/s^2');
qty = new Qty('1 m^2 s^-2'); // negative powers
qty = new Qty('1 m2 s-2'); // ^ is optional

qty = new Qty('1 m^2 kg^2 J^2/s^2 A');

qty = new Qty('1.5'); // unitless quantity
qty = new Qty(1.5); // number as initializing value

qty = new Qty('1 attoparsec/microfortnight');

qtyCopy = new Qty(qty); // quantity could be copied when used as
                        // initializing value

Parsing a quantity manually

Qty.parse utility method is also provided to parse and create quantities from strings. Unlike the constructor, it will return null instead of throwing an error when parsing an invalid quantity.

static parse(value: string): Qty

Qty.parse('1 m'); // => 1 meter
Qty.parse('foo'); // => null

Available well-known kinds

static getKinds(): string[]

Qty.getKinds(); // => Array of names of every well-known kind of units

Available units of a particular kind

static getUnits(kind?: string): string[]

Qty.getUnits('currency'); // => [ 'dollar', 'cents' ]
Qty.getUnits(); // All units, alphebetically sorted => [ 'acre','Ah','ampere','AMU','angstrom', ...]

Alternative names of a unit

static getAliases(unitName: string): string[]

Qty.getAliases('m'); // => [ 'm', 'meter', 'meters', 'metre', 'metres' ]

Quantity compatibility, kind and various queries

public isCompatible(other: Qty | string): boolean
qty1.isCompatible(qty2); // => true or false

public kind(): string
qty.kind(); // => 'length', 'area', etc...

public isUnitless(): boolean
qty.isUnitless(); // => true or false

public isBase(): boolean
qty.isBase(); // => true if quantity is represented with base units

Conversion

public toBase(): Qty
qty.toBase(); // converts to SI units (10 cm => 0.1 m) (new instance)

public toFloat(): number
qty.toFloat(); // returns scalar of unitless quantity
               // (otherwise throws error)

public to(Qty | string): Qty
qty.to('m'); // converts quantity to meter if compatible
             // or throws an error (new instance)
qty1.to(qty2); // converts quantity to same unit of qty2 if compatible
               // or throws an error (new instance)

public inverse(): Qty
qty.inverse(); // converts quantity to its inverse
               // ('100 m/s' => '0.01 s/m')
// Inverses can be used, but there is no special checking to
// rename the units
new Qty('10ohm').inverse(); // '0.1/ohm'
                       // (not '0.1S', although they are equivalent)
// however, the 'to' command will convert between inverses also
new Qty('10ohm').to('S'); // '0.1S'

public convertSingleUnit(baseUnit: string, targetUnit: string): Qty
// Converts the selected baseUnit into the target unit. Others units remain untouched.
new Qty('0.14 USD/kWh').convertSingleUnit('kWh', 'MWh'); // 140 USD/MWh
new Qty('4000 m2').convertSingleUnit('m', 'km'); // 0.004 km2

Mass conversion

Qty.swiftConverter() is a fast way to efficiently convert large array of Number values. It configures a function accepting a value or an array of Number values to convert.

static swiftConverter(srcUnits: string, dstUnits: string): (value: number | number[]) => number | number[]

const convert = Qty.swiftConverter('m/h', 'ft/s'); // Configures converter

// Converting single value
const converted = convert(2500); // => 2.278..
// Converting large array of values
const convertedArray = convert([2500, 5000, ...]); // => [2.278.., 4.556.., ...]

The main drawback of this conversion method is that it does not take care of rounding issues.

Comparison

public eq(other: Qty): boolean
qty1.eq(qty2); // => true if both quantities are equal (1m == 100cm => true)

public same(other: Qty): boolean
qty1.same(qty2); // => true if both quantities are same (1m == 100cm => false)

public lt(other: Qty): boolean
qty1.lt(qty2); // => true if qty1 is stricty less than qty2

public lte(other: Qty): boolean
qty1.lte(qty2); // => true if qty1 is less than or equal to qty2

public gt(other: Qty): boolean
qty1.gt(qty2); // => true if qty1 is stricty greater than qty2

public gte(other: Qty): boolean
qty1.gte(qty2); // => true if qty1 is greater than or equal to qty2

public compareTo(other: Qty): number
qty1.compareTo(qty2); // => -1 if qty1 < qty2,
                      // => 0 if qty1 == qty2,
                      // => 1 if qty1 > qty2

Operators

public add(other: Qty | string | number): Qty // other should be unit compatible.
public sub(other: Qty | string | number): Qty // other should be unit compatible.
public mul(other: Qty | string | number): Qty
public div(other: Qty | string | number): Qty

Rounding

Qty#toPrec(precision) : returns the nearest multiple of quantity passed as precision.

public toPrec(precQuantity: Qty | string | number): Qty

const qty = new Qty('5.17 ft');
qty.toPrec('ft'); // => 5 ft
qty.toPrec('0.5 ft'); // => 5 ft
qty.toPrec('0.25 ft'); // => 5.25 ft
qty.toPrec('0.1 ft'); // => 5.2 ft
qty.toPrec('0.05 ft'); // => 5.15 ft
qty.toPrec('0.01 ft'); // => 5.17 ft
qty.toPrec('0.00001 ft'); // => 5.17 ft
qty.toPrec('2 ft'); // => 6 ft
qty.toPrec('2'); // => 6 ft

const qty = new Qty('6.3782 m');
qty.toPrec('dm'); // => 6.4 m
qty.toPrec('cm'); // => 6.38 m
qty.toPrec('mm'); // => 6.378 m
qty.toPrec('5 cm'); // => 6.4 m
qty.toPrec('10 m'); // => 10 m
qty.toPrec(0.1); // => 6.3 m

const qty = new Qty('1.146 MPa');
qty.toPrec('0.1 bar'); // => 1.15 MPa

Formatting quantities

Qty#toString returns a string using the canonical form of the quantity (that is it could be seamlessly reparsed by Qty).

public toString(toUnits?: string): string

var qty = new Qty('1.146 MPa');
qty.toString(); // => '1.146 MPa'

As a shorthand, units could be passed to Qty#toString and is equivalent to successively call Qty#to then Qty#toString.

const qty = new Qty('1.146 MPa');
qty.toString('bar'); // => '11.46 bar'
qty.to('bar').toString(); // => '11.46 bar'

Qty#toString could also be used with any method from Qty to make some sort of formatting. For instance, one could use Qty#toPrec to fix the maximum number of decimals:

const qty = new Qty('1.146 MPa');
qty.toPrec(0.1).toString(); // => '1.1 MPa'
qty.to('bar').toPrec(0.1).toString(); // => '11.5 bar'

For advanced formatting needs as localization, specific rounding or any other custom customization, quantities can be transformed into strings through Qty#format according to optional target units and formatter. If target units are specified, the quantity is converted into them before formatting.

Such a string is not intended to be reparsed to construct a new instance of Qty (unlike output of Qty#toString).

If no formatter is specified, quantities are formatted according to default ts-quantities' formatter and is equivalent to Qty#toString.

type Formatter = (scalar: number, units: string) => string;
public format(formatter?: Formatter): string;
public format(targetUnits?: string, formatter?: Formatter): string;

var qty = new Qty('1.1234 m');
qty.format(); // same units, default formatter => '1.234 m'
qty.format('cm'); // converted to 'cm', default formatter => '123.45 cm'

Qty#format could delegates formatting to a custom formatter if required. A formatter is a callback function accepting scalar and units as parameters and returning a formatted string representing the quantity.

const configurableRoundingFormatter = (maxDecimals: number): Formatter => {
  return (scalar: number, units: string): string => {
    const pow = Math.pow(10, maxDecimals);
    const rounded = Math.round(scalar * pow) / pow;
    return rounded + ' ' + units;
  };
};

const qty = new Qty('1.1234 m');

// same units, custom formatter => '1.12 m'
qty.format(configurableRoundingFormatter(2));

// convert to 'cm', custom formatter => '123.4 cm'
qty.format('cm', configurableRoundingFormatter(1));

Custom formatter can be configured globally by setting Qty.formatter.

static formatter: Formatter;

Qty.formatter = configurableRoundingFormatter(2);
const qty = new Qty('1.1234 m');
qty.format(); // same units, current default formatter => '1.12 m'

Temperatures

Like ruby-units, ts-quantities makes a distinction between a temperature (which technically is a property) and degrees of temperature (which temperatures are measured in).

Temperature units (i.e., 'tempK') can be converted back and forth, and will take into account the differences in the zero points of the various scales. Differential temperature (e.g., '100 degC') units behave like most other units.

new Qty('37 tempC').to('tempF') // => 98.6 tempF

ts-quantities will throw an error if you attempt to create a temperature unit that would fall below absolute zero.

Unit math on temperatures is fairly limited.

new Qty('100 tempC').add('10 degC')  // 110 tempC
new Qty('100 tempC').sub('10 degC')  // 90 tempC
new Qty('100 tempC').add('50 tempC') // throws error
new Qty('100 tempC').sub('50 tempC') // 50 degC
new Qty('50 tempC').sub('100 tempC') // -50 degC
new Qty('100 tempC').mul(scalar)     // 100*scalar tempC
new Qty('100 tempC').div(scalar)     // 100/scalar tempC
new Qty('100 tempC').mul(qty)        // throws error
new Qty('100 tempC').div(qty)        // throws error
new Qty('100 tempC*unit')            // throws error
new Qty('100 tempC/unit')            // throws error
new Qty('100 unit/tempC')            // throws error
new Qty('100 tempC').inverse()       // throws error

new Qty('100 tempC').to('degC') // => 100 degC

This conversion references the 0 point on the scale of the temperature unit

new Qty('100 degC').to('tempC') // => -173.15 tempC

These conversions are always interpreted as being relative to absolute zero. Conversions are probably better done like this...

new Qty('0 tempC').add('100 degC') // => 100 tempC

Errors

Every error thrown by ts-quantities is an instance of Qty.Error.

try {
  // code triggering an error inside ts-quantities
}
catch(error) {
  if(error instanceof Qty.Error) {
    // ...
  }
  else {
    // ...
  }
}

Tests

Tests are implemented with Jasmine (https://github.com/pivotal/jasmine).

To execute specs through jasmine-node, launch:

npm install -g jasmine-node
npm run test

Contribute

Feedback and contributions are welcomed.

Pull requests must pass tests and linting. Please make sure that npm run test and npm run lint return no errors before submitting.