JS-quantities


JS-quantities is originally a JavaScript port of Kevin Olbrich's library Ruby
Units (http://github.com/olbrich/ruby-units).

The library aims to simplify the handling of units for scientific calculations
involving quantities.

JS-quantities is built as UMD and ES modules and can be used with Node.js
and browsers. It has no dependencies.

Installation

Install with npm install js-quantities or download latest release v1.8.0 as:

* UMD module
* ES module

Usage

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``javascript
// As CommonJS module
const Qty = require('js-quantities');

// As ES module
import Qty from 'js-quantities/esm';
`

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* UMD module could be included as is:

`html

`

In this case, it will define a global variable Qty.

* With an AMD loader like Require.JS:

`javascript
define(['quantities'], function(Qty) {
...
});
`

* As ES module:

`html

`

Synopsis

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Instances of quantities are made by means of Qty() method. Qty can both be
used as a constructor (with new) or as a factory (without new):

`javascript
qty = new Qty('23 ft'); // constructor
qty = Qty('23 ft'); // factory
`

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:

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

For the sake of simplicity, one will use the factory way below but using
new Qty() is equivalent.

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

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

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

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

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

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

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

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

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.

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

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

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`javascript
Qty.getUnits('currency'); // => [ 'dollar', 'cents' ]
// Or all alphabetically sorted
Qty.getUnits(); // => [ 'acre','Ah','ampere','AMU','angstrom']
`

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

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`javascript
qty1.isCompatible(qty2); // => true or false

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

qty.isUnitless(); // => true or false
qty.isBase(); // => true if quantity is represented with base units
`

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`javascript
qty.toBase(); // converts to SI units (10 cm => 0.1 m) (new instance)

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

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)

qty.inverse(); // converts quantity to its inverse
// ('100 m/s' => '.01 s/m')
// Inverses can be used, but there is no special checking to
// rename the units
Qty('10ohm').inverse() // '.1/ohm'
// (not '.1S', although they are equivalent)
// however, the 'to' command will convert between inverses also
Qty('10ohm').to('S') // '.1S'
`

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.

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

// Converting single value
var converted = convert(2500); // => 2.278..

// Converting large array of values
var convertedSerie = convert([2500, 5000, ...]); // => [2.278.., 4.556.., ...]
`

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

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`javascript
qty1.eq(qty2); // => true if both quantities are equal (1m == 100cm => true)
qty1.same(qty2); // => true if both quantities are same (1m == 100cm => false)
qty1.lt(qty2); // => true if qty1 is stricty less than qty2
qty1.lte(qty2); // => true if qty1 is less than or equal to qty2
qty1.gt(qty2); // => true if qty1 is stricty greater than qty2
qty1.gte(qty2); // => true if qty1 is greater than or equal to qty2

qty1.compareTo(qty2); // => -1 if qty1 < qty2,
// => 0 if qty1 == qty2,
// => 1 if qty1 > qty2
`

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* add(other): Add. other can be string or quantity. other should be unit compatible.
* sub(other): Substract. other can be string or quantity. other should be unit compatible.
* mul(other): Multiply. other can be string, number or quantity.
* div(other): Divide. other can be string, number or quantity.

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

`javascript
var qty = 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

var qty = 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

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

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

`javascript
var qty = 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.

`javascript
var qty = 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:

`javascript
var qty = 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
js-quantities' formatter and is equivalent to Qty#toString.

`javascript
var qty = 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.

`javascript
var configurableRoundingFormatter = function(maxDecimals) {
return function(scalar, units) {
var pow = Math.pow(10, maxDecimals);
var rounded = Math.round(scalar * pow) / pow;

return rounded + ' ' + units;
};
};

var qty = 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.

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

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Like ruby-units, JS-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.

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

JS-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.

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

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

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

`javascript
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...

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

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

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

Tests

Tests are implemented with Jasmine (https://github.com/pivotal/jasmine).
You could use both HTML and jasmine-node runners.

To execute specs through HTML runner, just open SpecRunner.html file in a
browser to execute them.

To execute specs through jasmine-node, launch:

make test

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There is a small benchmarking HTML page to spot performance regression between
currently checked-out quantities.js and any committed version.
Just execute:

make bench

then open http://0.0.0.0:3000/bench

Checked-out version is benchmarked against HEAD by default but it could be changed by passing
any commit SHA on the command line. Port (default 3000) is also configurable.

make bench COMMIT=e0c7fc468 PORT=5000

TypeScript type declarations

A TypeScript declaration file is published on
DefinitelyTyped.

It could be installed with npm install @types/js-quantities.

Contribute

Feedback and contributions are welcomed.

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