UnitMath is a JavaScript library for unit conversion and arithmetic.
- Install
- Getting Started
- Creating Units
- Unit Conversion
- Arithmetic
- Simplify
- Formatting
- Configuring
- Extending UnitMath
- API Reference
- Contributing
- Acknowledgements
- License
npm install unitmath
const unit = require('unitmath')
let a = unit('5 m').div('2 s') // 2.5 m / s
let b = unit('40 km').to('mile') // 24.8548476894934 mile
b.toString({ precision: 4 }) // "24.85 mile"
To create a unit, call unit
with either a single string, or a number and a string:
// String
let a = unit('40 mile')
let b = unit('hour')
// Number and string
let g = unit(9.8, 'm/s^2')
let h = unit(19.6, 'm')
Units can be simple (4 kg
) or compound (8.314 J/mol K
). They may also be valueless (hour
).
Parsing rules are different than typical JavaScript syntax. For instance:
- The string may only contain one
"/"
. Units appearing before the/
will be in the numerator of the resulting unit, and units appearing after the/
will be in the denominator. - Parentheses
()
and asterisk*
are ignored: multiplication is implicit. - Extra whitespace is allowed.
The following all form valid units:
// These are valid:
unit("2 in")
unit("60/s")
unit("8.314 * kg * m^2 / (s^2 * mol * K)")
unit("6.022e-23 mol^-1")
unit("kW / kg K")
unit("3.1415926535897932384626433832795 rad")
// These are invalid:
unit("2 in + 3 in") // Unexpected "+" (Use .add() instead)
unit("60 / s / s") // Unexpected additional "/"
unit("0x123 kg") // Unit "x123" not found
The exact syntax is as follows:
[value][numerator][/denominator]
numerator, denominator:
atomicUnit [atomicUnit ...]
atomicUnit:
[prefix]unit[^power]
value, power:
Any floating-point number
unit, prefix:
Any built-in or user-defined unit or prefix
The to
method converts from one unit to another. The two units must have the same dimension.
// Convert units
unit('40 km').to('mile') // 24.8548476894934 mile
unit('kg').to('lbm') // 2.20462262184878 lbm
unit(5000, 'kg').to('N s') // Cannot convert 5000 kg to N s: dimensions do not match
The split
method will convert one unit into an array of units like so:
// Split a unit into parts
unit('10 km').split([ 'mi', 'ft', 'in' ]) // [ 6 mi, 1128 ft, 4.78740157486361 in ]
unit('51.4934 deg').split([ 'deg', 'arcmin', 'arcsec' ]) // [ 51 deg, 29 arcmin, 36.24 arcsec ]
Use the methods add
, sub
, mul
, div
, pow
, sqrt
, and others to perform arithmetic on units. Multiple operations can be chained together:
// Chain operations together
let g = unit(9.8, 'm/s^2')
let h = unit(19.6, 'm')
h.mul(2).div(g).sqrt() // 2 s
Strings and numbers are implicitly converted to units within a chained expression. When chaining operators, they will execute in order from left to right. This may not be the usual, mathematical order of operations:
// Strings are implicitly converted to units
unit('3 ft').add('6 in').mul(2) // 7 ft
All of the operators are also available on the top-level unit
object as static functions:
// Using static functions
unit.mul(unit.add('3 ft', '6 in'), 2) // 7 ft
Units are immutable, so every operation on a unit creates a new unit.
UnitMath has a simplify
method that will attempt to simplify a unit:
// Simplify units
unit('10 / s').simplify() // 10 Hz
unit('J / m').simplify() // N
Because units are immutable, simplify
always returns a new unit with the simplified units. It does not modify the original unit.
In the simplify
method, simplification is performed in two steps:
- Attempting to simplify a compound unit into a single unit in the desired unit system
- Choosing an appropriate prefix (if
options.autoPrefix
is true)
Here are the options available for the simplify
method:
-
system
- Default:'auto'
. The unit system to use when simplifying aunit
. Available systems aresi
,cgs
,us
, andauto
.// Simplify units using a specific system unit('8 kg m / s^2').simplify({ system: 'si' }) // 8 N unit('8 kg m / s^2').simplify({ system: 'cgs' }) // 800 kdyn unit('8 kg m / s^2').simplify({ system: 'us' }) // 1.79847154479768 lbf
When
system
is'auto'
(the default), UnitMath will try to infer the unit system from the individual units that make up thatunit
. This is not guaranteed to succeed in all cases, so whenever possible, the system should be specified explicitly.unit = unit.config({ system: 'auto' }) // Automatically infer the unit system while simplifying unit('150 lbf').div('10 in^2').simplify() // 15 psi unit('400 N').div('10 cm^2').simplify() // 400 kPa
Specifying a unit system other than
'auto'
will force UnitMath to use the specified system. Use theconfig
function to apply the system everywhere, or pass a configuration object tosimplify
to apply to a single statement:unit = unit.config({ system: 'us' }) let a = unit('5 m').div('2 s') a.simplify() // 8.202099737532809 ft / s // Override the system for this statement a.simplify({ system: 'si'}) // 2.5 m / s
-
autoPrefix
- Default:true
. This option specifies whethersimplify
will try to choose an appropriate prefix in case of very small or very large quantities.unit('1e-10 kg m / s^2').simplify() // 0.0001 uN unit('1e-10 kg m / s^2').simplify({ autoPrefix: false }) // 1e-10 N
-
prefixMin
andprefixMax
- Defaults:0.1
and1000
. Sets the threshold for choosing a different prefix whenautoPrefix
is true.unit('0.005 m').simplify() // 0.5 cm unit('0.005 m').simplify({ prefixMin: 0.001 }) // 0.005 m
-
formatPrefixDefault
- Default:none
. By default, certain units are never assigned a new prefix (this is controlled by theformatPrefixes
property of the unit definition.) By settingformatPrefixDefault
to"all"
, this behavior can be changed.unit('1000001 lumen').simplify() // 1000001 lumen unit('1000001 lumen').simplify({ formatPrefixDefault: 'all' }) // 1.000001 megalumen
Use toString
to output a unit as a string:
unit('1 lb').to('kg').toString() // "0.45359237 kg"
The toString
method accepts a configuration object. The following options are available:
-
precision
- Default:15
. The number of significant figures to output when converting a unit to a string. Reducing this can help reduce the appearance of round-off errors. Setting a value of 0 will disable rounding.// Output a unit with a specific precision unit('180 deg').to('rad').toString({ precision: 6 }) // 3.14159 rad unit('1 lb').to('kg').toString({ precision: 4 }) // "0.4536 kg"
-
parentheses
- Default:false
. When formatting a unit, group the numerator and/or denominator in parentheses if multiple units are present. This is useful when the resulting string will be used in a mathematical expression.// Output a unit with parentheses unit('45 W / m K').toString({ parentheses: true }) // 45 W / (m K)
-
formatter
. Define a custom formatter for the numeric portion of the unit. The formatter will be passed the numeric value of the unit. For example:let unit = require('unitmath') // Custom formatter let formatter = new Intl.NumberFormat('en-US', { style: 'currency', currency: 'USD', }); // Specify formatter in argument to toString unit('25000 / ton').toString({ formatter: formatter.format }) // "$25,000.00 ton^-1" // Specify formatter in config let unitMoney = unit.config({ formatter: formatter.format }) unitMoney('25000 / ton').toString() // "$25,000.00 ton^-1"
The toString
method outputs a unit exactly as it is represented internally. It does not automatically simplify a unit. This means you will usually want to call simplify
before calling toString
. How and when to simplify a unit is very subjective. UnitMath cannot anticipate all needs, so the user must explicitly call simplify
when needed.
// toString outputs units "as-is".
unit('10 / s').toString() // "10 s^-1"
unit('10 / s').simplify().toString() // "10 Hz"
UnitMath can be configured using unit.config(options)
. The function returns a new instance of UnitMath with the specified configuration options.
// Set the default unit system to "us"
const unit = require('unitmath').config({ system: 'us' })
Available options are:
-
Any of the simplify options.
-
Any of the formatting options.
-
type
. An object that allows UnitMath to work with custom numeric types. See Custom Types for complete details and examples. -
definitions
. An object that allows you to add to, modify, or remove the built-in units. See User-Defined Units for complete details.// Create a new configuration unit = unit.config({ definitions: { units: { furlong: { value: '220 yards' }, fortnight: { value: '2 weeks' } } }, precision: 6 }) unit('6 furlong/fortnight').to('m/s') // 0.000997857 m / s
Because unit.config(options)
returns a new instance of UnitMath, is is technically possible to perform operations between units created from different instances. The resulting behavior is undefined, however, so it is probably best to avoid doing this.
Important: unit.config(options)
returns a new instance of the factory function, so you must assign the return value of unit.config(options)
to some variable, otherwise the new options won't take effect:
let unit = require('unitmath')
// Incorrect, has no effect!
unit.config(options)
// Correct
unit = unit.config(options)
Call unit.getConfig()
to return the current configuration.
// Get the current configuration
unit.getConfig() // { system: 'si', ... }
To create a user-defined unit, pass an object with a definitions
property to unit.config()
:
// Create a new configuration adding a user-defined unit
unit = unit.config({
definitions: {
units: {
lightyear: { value: '9460730472580800 m' }
}
}
})
unit('1 lightyear').to('mile') // 5878625373183.61 mile
The definitions
object contains four properties which allow additional customization of the unit system: units
, prefixGroups
, systems
, and skipBuiltIns
.
definitions.units
This object contains the units that are made available by UnitMath. Each key in definitions.units
becomes a new unit. The easiest way to define a unit is to provide a string representation in terms of other units:
// Define new units in terms of existing ones
definitions: {
units: {
minute: { value: '60 seconds' },
newton: { value: '1 kg m/s^2' }
}
}
Here are all the options you can specify:
-
value
: (Required) The value of the unit. It can be a string or an array containing two items:// value can be a string... definitions: { units: { minute: { value: '60 seconds' }, newton: { value: '1 kg m/s^2' } } } // ...or an array. definitions: { units: { minute: { value: [ 60, 'seconds' ] }, newton: { value: [ 1, 'kg m/s^2' ] } } }
-
quantity
: Specifying aquantity
will create a new base unit. This is required for units that are not defined in terms of other units, such asmeter
andsecond
. In this case,value
will just be a number (or custom type):// Specify `quantity` creates a new base unit definitions: { units: { seconds: { quantity: 'TIME', value: 1 } } }
Only use
quantity
to define base units. Do not usequantity
to define a derived unit:// Incorrect definitions: { units: { meter: { quantity: 'LENGTH', value: 1 }, squareMeter: { quantity: 'LENGTH^2', value: 1 } } } // Correct definitions: { units: { meter: { quantity: 'LENGTH', value: 1 }, squareMeter: { value: '1 meter^2' } } }
-
prefixGroup
- Default:'NONE'
. Specifies which prefix group will be used when parsing and formatting the unit.definitions: { units: { // Will parse 'nanometer', 'micrometer', 'millimeter', 'kilometer', 'megameter', etc. meter: { prefixGroup: 'LONG', ... }, // Will parse 'nm', 'um', 'mm', 'km', 'Mm', etc. m: { prefixGroup: 'SHORT', ... } } }
-
formatPrefixes
: A string array that specifies individual items of the unit's prefix group which will be used when formatting a unit. If this option is omitted, the global optionformatPrefixDefault
determines whether the unit will be formatted using all prefixes in the prefix group, or none at all.definitions: { units: { L: { value: '1e-3 m^3' // Parse any prefix in the 'SHORT' prefix group prefixGroup: 'SHORT', // Format only as 'nL', 'uL', 'mL', and 'L'. formatPrefixes: ['n', 'u', 'm', ''], }, lumen: { value: '1 cd sr' // Parse any prefix in the 'LONG' prefix group prefixGroup: 'LONG', // formatPrefixes is not given, so lumen will be formatted // only as "lumen" if formatPrefixDefault === false, // or formatted using any of the prefixes in the 'LONG' // prefix group if formatPrefixDefault === true. } } }
-
basePrefix
: Optional. The prefix to use for a base unit, if the base unit has one. This is necessary for units such as kilogram, which is a base unit but has a prefix.// Special case for base units with prefixes, such as kg definitions: { units: { g: { quantity: 'MASS', prefixGroup: 'SHORT', formatPrefixes: ['n', 'u', 'm', '', 'k'], value: 0.001, // Treat as if 'kg' is the base unit, not 'g' basePrefix: 'k' } } }
-
aliases
: Shortcut to create additional units with identical definitions.// Create aliases for a unit definitions: { units: { meter: { ... , aliases: [ 'meters' ] } } }
-
offset
- Default:0
: Used when the zero-value of this unit is different from the zero-value of the base unit.// Special case for units with an offset from the base unit, like celsius definitions: { units: { celsius: { value: '1 K', offset: 273.15 } } }
definitions.prefixGroups
The definitions.prefixGroups
object is used to define strings and associated multipliers that are prefixed to units to change their value. For example, the 'k'
prefix in km
multiplies the value of the m
unit by 1000.
For example:
// Define prefix groups
definitions: {
prefixGroups: {
NONE: { '': 1 },
SHORT: {
m: 0.001,
'': 1,
k: 1000
},
LONG: {
milli: 0.001,
'': 1,
kilo: 1000
}
}
}
definitions.systems
This object assigns one or more units to a number of systems. Each key in definitions.systems
becomes a system. For each system, list all the units that should be associated with that system in an array. The units may be single or compound (m
or m/s
) and may include prefixes.
Example:
// Define unit systems
definitions: {
systems: {
si: ['m', 'kg', 's', 'N', 'J', 'm^3', 'm/s'],
cgs: ['cm', 'g', 's', 'dyn', 'erg', 'cm^3', 'cm/s'],
us: ['ft', 'lbm', 's', 'lbf', 'btu', 'gal', 'ft/s']
}
}
When UnitMath formats a unit, it will try to use one of the units from the specified system.
definitions.skipBuiltIns
A boolean value indicating whether to skip the built-in units. If true
, only the user-defined units, prefix groups, and systems that are explicitly included in definitions
will be created.
// Skip built-in units: only the user-defined units,
// prefix groups, and systems will be created
definitions: {
skipBuiltIns: true
}
You can view all the current definitions by calling unit.definitions()
. This object contains all the units, prefix groups, and systems that you have configured, including the built-ins (unless definitions.skipBuiltIns
is true).
unit.definitions()
Below is an abbreviated sample output from unit.definitions()
. It can serve as a starting point to create your own definitions.
// Sample `definitions` config
{
units: {
'': { quantity: 'UNITLESS', value: 1 },
meter: {
quantity: 'LENGTH',
prefixGroup: 'LONG',
formatPrefixes: [ 'nano', 'micro', 'milli', 'centi', '', 'kilo' ],
value: 1,
aliases: [ 'meters' ]
},
m: {
prefixGroup: 'SHORT',
formatPrefixes: [ 'n', 'u', 'm', 'c', '', 'k' ],
value: '1 meter'
},
inch: { value: '0.0254 meter', aliases: [ 'inches', 'in' ] },
foot: { value: '12 inch', aliases: [ 'ft', 'feet' ] },
yard: { value: '3 foot', aliases: [ 'yd', 'yards' ] },
mile: { value: '5280 ft', aliases: [ 'mi', 'miles' ] },
...
},
prefixGroups: {
NONE: { '': 1 },
SHORT: {
'': 1,
da: 10,
h: 100,
k: 1000,
...
d: 0.1,
c: 0.01,
m: 0.001,
...
},
},
systems: {
si: ['m', 'meter', 's', 'A', 'kg', ...],
cgs: ['cm', 's', 'A', 'g', 'K', ...],
us: ['ft', 's', 'A', 'lbm', 'degF', ...]
}
}
You can extend UnitMath to work with custom types. The type
option is an object containing several properties, where each property value is a function that replaces the normal +
, -
, *
, /
, and other arithmetic operators used internally by UnitMath.
Example using Decimal.js as the custom type:
// Configure UnitMath to use Decimal.js
const Decimal = require('decimal.js')
const unit = unit.config({
type: {
clone: (x) => new Decimal(x),
conv: (x) => new Decimal(x),
add: (a, b) => a.add(b),
sub: (a, b) => a.sub(b),
mul: (a, b) => a.mul(b),
div: (a, b) => a.div(b),
pow: (a, b) => a.pow(b),
eq: (a, b) => a.eq(b),
lt: (a, b) => a.lt(b),
le: (a, b) => a.lte(b),
gt: (a, b) => a.gt(b),
ge: (a, b) => a.gte(b),
abs: (a) => a.abs(),
round: (a) => a.round(),
trunc: (a) => Decimal.trunc(a)
}
})
let u = unit2('2.74518864784926316174649567946 m')
Below is a table of functions, their description, and when they are required:
Function | Description | Required? |
---|---|---|
clone: (a: T) => T |
Create a new instance of the custom type. | Always |
conv: (a: number | string | T) => T |
Convert a number or string into the custom type. | Always |
add: (a: T, b: T) => T |
Add two custom types. | Always |
sub: (a: T, b: T) => T |
Subtract two custom types. | Always |
mul: (a: T, b: T) => T |
Multiply two custom types. | Always |
div: (a: T, b: T) => T |
Divide two custom types. | Always |
pow: (a: T, b: number) => T |
Raise a custom type to a power. | Always |
abs: (a: T) => T |
Return the absolute value of a custom type. | For autoPrefix: true |
lt: (a: T, b: T) => boolean |
Compare two custom types for less than. | For autoPrefix: true |
le: (a: T, b: T) => boolean |
Compare two custom types for less than or equal. | For autoPrefix: true |
gt: (a: T, b: T) => boolean |
Compare two custom types for greater than. | For autoPrefix: true |
ge: (a: T, b: T) => boolean |
Compare two custom types for greater than or equal. | For autoPrefix: true |
eq: (a: T, b: T) => boolean |
Compare two custom types for equality. | For the equals function |
round: (a: T) => T |
Round a custom type to the nearest integer. | For the split function |
trunc: (a: T) => T |
Truncate a custom type to the nearest integer. | For the split function |
The add
, sub
, mul
, div
, and pow
functions replace +
, -
, *
, /
, and Math.pow
, respectively. The clone
function should return a clone of your custom type (same value, different object).
The conv
function must, at a minimum, be capable of converting both strings and numbers into your custom type. If given a custom type, it should return it unchanged, or return a clone. Among other things, the conv
function is used by UnitMath to convert the values of the built-in units to your custom type during initialization.
UnitMath will also use the conv
function when constructing units from numbers and strings. If your custom type is representable using decimal or scientific notation (such as 6.022e+23
), you can include both the value and the units in a single string:
// Supply a single string, and the numeric portion will be parsed using type.conv
unit('3.1415926535897932384626433832795 rad')
If your custom type cannot be represented in decimal or scientific notation, such as is the case with complex numbers and fractions, you will have to pass your custom type and the unit string separately:
unit(Fraction(1, 2), 'kg')
The functions clone
, conv
, add
, sub
, mul
, div
, and pow
are always required. Omitting any of these will cause the config
method to throw an error. The other functions are conditionally required, and you will receive an error if you attempt something that depends on a function you haven't provided.
In the function signatures below, the T
type is the custom type you have provided, or number
if you have not provided a custom type.
-
unit(value: T, unitString: string): unit
unit(value: T): unit
unit(valueAndUnitString: string): unit
unit(): unit
Creates a unit with the specified value and unit string. If
valueAndUnitString
is supplied, it must specify both the numeric portion and the units portion of the unit.const unit = require('unitmath') unit(60, 'mile/hour') // 60 mile / hour unit(60) // 60 unit('60 mile/hour') // 60 mile / hour unit('mile/hour') // mile / hour unit() // Empty unit
unit()
will parse the special strings"NaN"
,"Infinity"
, and"-Infinity"
as the corresponding numeric values:const unit = require('unitmath') unit('Infinity kg') // Infinity kg
The string used to specify the unit (
valueAndUnitString
orunitString
) must be in the following format:[value][numerator][/denominator] numerator, denominator: atomicUnit [atomicUnit ...] atomicUnit: [prefix]unit[^power] value: Any floating-point number, or the strings "NaN", "Infinity", or "-Infinity" (without the quotes). power: Any floating-point number
-
add(other: unit | string | T) : unit
Adds another unit to this unit. If a string or number is supplied as an argument, it is converted to a unit. Both units must have values and have matching dimensions.
let a = unit('20 kW') let b = unit('300 W') let sum = a.add(b) // 20.3 kW
-
sub(other: unit | string | T) : unit
Subtract another unit from this unit. If a string or number is supplied as an argument, it is converted to a unit. Both units must have values and have matching dimensions.
let a = unit('4 ft') let b = unit('1 yd') let difference = a.sub(b) // 1 ft
-
mul(other: unit | string | T) : unit
Multiplies this unit by another unit. If a string or number is supplied as an argument, it is converted to a unit.
let a = unit('8 m') let b = unit('200 N') let product = a.mul(b).simplify() // 1.6 kJ
-
div(other: unit | string | T) : unit
Divides this unit by another unit. If a string or number is supplied as an argument, it is converted to a unit.
let a = unit('64 kJ') let b = unit('16 s') let quotient = a.div(b).simplify() // 4 kW
-
pow(p: number)
Raises this unit to the power
p
and returns a new unit.let result = unit('10 m').pow(3) // 1000 m^3
-
sqrt()
Returns the square root of this unit.
unit('1 hectare').sqrt().simplify() // 100 m
-
abs()
Returns the absolute value of this unit. If this unit has an offset, such as
degC
, this is applied before taking the absolute value.unit('-5 m / s').abs() // 5 m / s unit('-293.15 degC').abs() // -253.15 degC
-
clone()
Clones this unit.
let unit = require('unitmath') let a = unit('40 m/s') // 40 m / s let b = a.clone() // 40 m / s
-
to(target: unit | string)
Converts this unit to the specified target unit or string. The returned unit will be "fixed", so it will not be auto-simplified or auto-prefixed in
format()
.let r = unit('10 kg m^2 / s^3 A^2') r.simplify().toString() // 10 ohm r.to('kohm').toString() // 0.01 kohm
-
toBaseUnits()
Returns a new unit in the base representation.
unit('10 ft/s').toBaseUnits() // 3.048 m / s
-
getValue()
Returns the value of this unit, or
null
if the unit is valueless.unit('70 mile/hour').getValue() // 70 unit('km / hour').getValue() // null
-
setValue(x: number | string | custom)
Returns a copy of this unit but with its value replaced with the given value. Useful if you would like to perform your own operations on a unit's value. If supplied with no arguments, or
null
, will remove the value from the unit.unit('10 m').setValue(20) // 20 m unit('m').setValue(20) // 20 m unit('10 ft').setValue(20) // 20 ft unit('10 ft').setValue() // ft
-
getNormalizedValue()
Returns the value of this unit if it were to be converted to SI base units (or whatever base units that are defined). Returns
null
if the unit is valueless.unit('10 ft/s').getNormalizedValue() // 3.048
-
setNormalizedValue()
Returns a copy of this unit but with its value replaced with the given normalized value.
unit('ft / s').setNormalizedValue(3.048) // 10 ft / s
-
simplify()
Attempts to simplify this unit, and returns the simplified unit (or a clone of the original if unsuccessful).
simplify()
is called when a unit is being formatted as a string whenever the config optionsimplify
is'auto'
or'always'
.unit('10 N m').simplify() // 10 J
-
split(Array(string | unit))
Returns an array of units that result from splitting this unit into the given units. The sum of the resulting units is equal to this unit, and each of the returned units is the result of truncating this unit to an integer, and then passing the remainder to the next unit, until the final unit, which takes up all the remainder.
unit('51.4934 deg').split([ 'deg', 'arcmin', 'arcsec' ]) // [ 51 deg, 29 arcmin, 36.24 arcsec ]
-
getUnits()
Returns a clone of this unit with the value removed. Equivalent to
unit.setValue(null)
.unit('8.314 J / mol K').getUnits() // J / mol K
-
isCompound()
Returns true if this unit's unit list contains two or more units, or one unit with a power not equal to 1.
unit('34 kg').isCompound() // false unit('34 kg/s').isCompound() // true unit('34 kg^2').isCompound() // true unit('34 N').isCompound() // false unit('34 kg m / s^2').isCompound() // true
-
isBase()
Returns true if this unit's unit list contains exactly one unit with a power equal to 1, and which is the of same dimension as one of the base dimensions length, time, mass, etc., or a user-defined base dimension.
unit = unit.config({ definitions: { units: { myUnit: { quantity: 'MY_NEW_BASE', value: 1 }, anotherUnit: { value: '4 myUnit' } } } }) unit('34 kg').isBase() // true unit('34 kg/s').isBase() // false unit('34 kg^2').isBase() // false unit('34 N').isBase() // false unit('34 myUnit').isBase() // true unit('34 anotherUnit').isBase() // true
-
getInferredSystem()
Examines this unit's unitList to determine the most likely system this unit is expressed in.
unit('10 N m').getInferredSystem() // 'si' unit('10 J / m').getInferredSystem() // 'si' unit('10 m^3 Pa').getInferredSystem() // 'si' unit('10 dyne/cm').getInferredSystem() // 'cgs' unit('10 ft/s').getInferredSystem() // 'us' unit('10').getInferredSystem() // null
-
equalsQuantity(other: unit | string)
Returns true if this unit and another unit have equal quantities or dimensions.
unit('5 m/s^2').equalsQuantity('4 ft/s^2') // true
-
equals(other: unit | string)
Returns true if the two units represent the same values.
unit('3 ft').equals('1 yard') // true
-
compare(other: unit | string)
Returns a value indicating whether this unit is less than (-1), greater than (1), or equal to (0), another unit.
unit('30 min').compare('1 hour') // -1 unit('60 min').compare('1 hour') // 0 unit('90 min').compare('1 hour') // 1
-
lessThan(other: unit | string)
Compares this and another unit and returns true if this unit is less than the other.
unit('80 cm').lessThan('1 m') // true unit('100 cm').lessThan('1 m') // false unit('120 cm').lessThan('1 m') // false
-
lessThanOrEqual(other: unit | string)
Compares this and another unit and returns true if this unit is less than or equal to the other.
unit('80 cm').lessThanOrEqual('1 m') // true unit('100 cm').lessThanOrEqual('1 m') // true unit('120 cm').lessThanOrEqual('1 m') // false
-
greaterThan(other: unit | string)
Compares this and another unit and returns true if this unit is greater than the other.
unit('80 cm').greaterThan('1 m') // false unit('100 cm').greaterThan('1 m') // false unit('120 cm').greaterThan('1 m') // true
-
greaterThanOrEqual(other: unit | string)
Compares this and another unit and returns true if this unit is greater than or equal to the other.
unit('80 cm').greaterThanOrEqual('1 m') // false unit('100 cm').greaterThanOrEqual('1 m') // true unit('120 cm').greaterThanOrEqual('1 m') // true
-
toString(options)
Formats this unit as a string. Formatting options can be supplied which will override the configured options. See Formatting for a list of all options and their effects.
-
add(a: unit | string | T, b: unit | string | T) : unit
Adds two units. If a string or number is supplied as an argument, it is converted to a unit. Both units must have values and have matching dimensions.
let sum = unit.add('20 kW', '300 W') // 20.3 kW
-
sub(a: unit | string | T, b: unit | string | T) : unit
Subtract two units. If a string or number is supplied as an argument, it is converted to a unit. Both units must have values and have matching dimensions.
let difference = unit.sub('4 ft', '1 yd') // 1 ft
-
mul(a: unit | string | T, b: unit | string | T) : unit
Multiplies two units. If a string or number is supplied as an argument, it is converted to a unit.
let product = unit.mul('8 m/s', '200 N').simplify() // 1.6 kW
-
div(a: unit | string | T, b: unit | string | T) : unit
Divides two units. If a string or number is supplied as an argument, it is converted to a unit.
let quotient = unit.div('64 kJ', '16 s').simplify() // 4 kW
-
pow(a: unit | string | T, p: number) : unit
Raises a unit to the power
p
and returns a new unit.let result = unit.pow('10 m', 3) // 1000 m^3
-
sqrt(a: unit | string | T) : unit
Returns the square root of a unit.
unit.sqrt('1 hectare').simplify() // 100 m
-
abs(a: unit | string | T) : unit
Returns the absolute value of a unit. If the unit has an offset, such as
degC
, this is applied before taking the absolute value.unit.abs('-5 m / s') // 5 m / s unit.abs('300 degC') // -246.3 degC
-
to(a: unit | string | number, b: unit | string)
Converts a unit to the specified target unit or string. The returned unit will be "fixed", so it will not be auto-simplified or auto-prefixed in
format()
.unit.to('10 kg m^2 / s^3 A^2', 'kohm') // 0.01 kohm
-
config(options:object)
Configure a new unit namespace with the given options (see Configuring)
const unit = require('unitmath').config({ option1, option2, ... })
-
getConfig()
Returns the current configuration.
const unit = require('unitmath') unit.getConfig()
-
exists(singleUnitString:string)
Tests if the given unit, optionally with a prefix, exists.
const unit = require('unitmath') unit.exists('km') // true
-
definitions()
Return the current unit definitions in effect. (User's own definitions can be queried through
unit.getConfig().definitions
.)
This is a community-supported project; all contributions are welcome. Please open an issue or submit a pull request.
Many thanks to Jos de Jong (@josdejong), the original author of Unit.js
, who suggested the idea of splitting the file off from Math.js and into its own library.
- Harry Sarson (https://github.com/harrysarson)
- Nick Ewing (https://github.com/nickewing)
- Michal Grňo (https://github.com/m93a)
UnitMath is released under the Apache-2.0 license.