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# postcss-calc [](https://travis-ci.org/postcss/postcss-calc)
> [PostCSS](https://github.com/postcss/postcss) plugin to reduce `calc()`.
This plugin reduce `calc()` references whenever it's possible.
This can be particularly useful with the [postcss-custom-properties](https://github.com/postcss/postcss-custom-properties) plugin.
**Note:** When multiple units are mixed together in the same expression, the `calc()` statement is left as is, to fallback to the [w3c calc() feature](http://www.w3.org/TR/css3-values/#calc).
## Installation
```console
$ npm install postcss-calc
```
## Usage
```js
// dependencies
var fs = require("fs")
var postcss = require("postcss")
var calc = require("postcss-calc")
// css to be processed
var css = fs.readFileSync("input.css", "utf8")
// process css
var output = postcss()
.use(calc())
.process(css)
.css
```
**Example** (with [postcss-custom-properties](https://github.com/postcss/postcss-custom-properties) enabled as well):
```js
// dependencies
var fs = require("fs")
var postcss = require("postcss")
var customProperties = require("postcss-custom-properties")
var calc = require("postcss-calc")
// css to be processed
var css = fs.readFileSync("input.css", "utf8")
// process css
var output = postcss()
.use(customProperties())
.use(calc())
.process(css)
.css
```
Using this `input.css`:
```css
:root {
--main-font-size: 16px;
}
body {
font-size: var(--main-font-size);
}
h1 {
font-size: calc(var(--main-font-size) * 2);
height: calc(100px - 2em);
margin-bottom: calc(
var(--main-font-size)
* 1.5
)
}
```
you will get:
```css
body {
font-size: 16px
}
h1 {
font-size: 32px;
height: calc(100px - 2em);
margin-bottom: 24px
}
```
Checkout [tests](test) for more examples.
### Options
#### `precision` (default: `5`)
Allow you to definine the precision for decimal numbers.
```js
var out = postcss()
.use(calc({precision: 10}))
.process(css)
.css
```
#### `preserve` (default: `false`)
Allow you to preserve calc() usage in output so browsers will handle decimal precision themselves.
```js
var out = postcss()
.use(calc({preserve: true}))
.process(css)
.css
```
#### `warnWhenCannotResolve` (default: `false`)
Adds warnings when calc() are not reduced to a single value.
```js
var out = postcss()
.use(calc({warnWhenCannotResolve: true}))
.process(css)
.css
```
#### `mediaQueries` (default: `false`)
Allows calc() usage as part of media query declarations.
```js
var out = postcss()
.use(calc({mediaQueries: true}))
.process(css)
.css
```
#### `selectors` (default: `false`)
Allows calc() usage as part of selectors.
```js
var out = postcss()
.use(calc({selectors: true}))
.process(css)
.css
```
Example:
```css
div[data-size="calc(3*3)"] {
width: 100px;
}
```
---
## Contributing
Work on a branch, install dev-dependencies, respect coding style & run tests before submitting a bug fix or a feature.
```console
$ git clone https://github.com/postcss/postcss-calc.git
$ git checkout -b patch-1
$ npm install
$ npm test
```
## [Changelog](CHANGELOG.md)
## [License](LICENSE)
|
