|
1 | | -# postcss-custom-functions |
| 1 | +# @yuheiy/postcss-custom-functions |
| 2 | + |
| 3 | +[PostCSS](https://github.com/postcss/postcss) plugin that allows users to define custom functions using JavaScript. This plugin is inspired by [custom functions](https://drafts.csswg.org/css-mixins-1/#custom-function) in CSS. |
| 4 | + |
| 5 | +For example, define a custom function: |
| 6 | + |
| 7 | +```js |
| 8 | +module.exports = { |
| 9 | + plugins: { |
| 10 | + '@yuheiy/postcss-custom-functions': { |
| 11 | + functions: { |
| 12 | + '--negative': (value) => `calc(-1 * ${value})`, |
| 13 | + }, |
| 14 | + }, |
| 15 | + }, |
| 16 | +}; |
| 17 | +``` |
| 18 | + |
| 19 | +Use the custom function you have defined: |
| 20 | + |
| 21 | +```css |
| 22 | +html { |
| 23 | + --gap: 1em; |
| 24 | + padding: --negative(var(--gap)); |
| 25 | + /* or by passing the value explicitly, like: */ |
| 26 | + padding: --negative(1em); |
| 27 | +} |
| 28 | +``` |
| 29 | + |
| 30 | +will be processed to: |
| 31 | + |
| 32 | +```css |
| 33 | +html { |
| 34 | + --gap: 1em; |
| 35 | + padding: calc(-1 * var(--gap)); |
| 36 | + /* or by passing the value explicitly, like: */ |
| 37 | + padding: calc(-1 * 1em); |
| 38 | +} |
| 39 | +``` |
| 40 | + |
| 41 | +## Usage |
| 42 | + |
| 43 | +**Step 1:** Install plugin: |
| 44 | + |
| 45 | +```sh |
| 46 | +npm install --save-dev postcss @yuheiy/postcss-custom-functions |
| 47 | +``` |
| 48 | + |
| 49 | +**Step 2:** Check you project for existed PostCSS config: `postcss.config.js` |
| 50 | +in the project root, `"postcss"` section in `package.json` |
| 51 | +or `postcss` in bundle config. |
| 52 | + |
| 53 | +If you do not use PostCSS, add it according to [official docs](https://github.com/postcss/postcss#usage) |
| 54 | +and set this plugin in settings. |
| 55 | + |
| 56 | +**Step 3:** Add the plugin to plugins list: |
| 57 | + |
| 58 | +```diff |
| 59 | +module.exports = { |
| 60 | + plugins: { |
| 61 | ++ '@yuheiy/postcss-custom-functions': {}, |
| 62 | + 'autoprefixer': {}, |
| 63 | + }, |
| 64 | +}; |
| 65 | +``` |
| 66 | + |
| 67 | +## Options |
| 68 | + |
| 69 | +### `functions` |
| 70 | + |
| 71 | +Type: `{ [key: string]: (...values: string[]) => string }` |
| 72 | +Default: `{}` |
| 73 | + |
| 74 | +Define custom functions that can be used in your CSS. |
| 75 | + |
| 76 | +## Tips |
| 77 | + |
| 78 | +### Optional arguments with fallback |
| 79 | + |
| 80 | +You can define custom functions with optional arguments and fallback values. |
| 81 | + |
| 82 | +```js |
| 83 | +function shadow(shadowColor) { |
| 84 | + return `2px 2px ${shadowColor ? shadowColor : 'var(--shadow-color, black)'}`; |
| 85 | +} |
| 86 | + |
| 87 | +module.exports = { |
| 88 | + plugins: { |
| 89 | + '@yuheiy/postcss-custom-functions': { |
| 90 | + functions: { |
| 91 | + '--shadow': shadow, |
| 92 | + }, |
| 93 | + }, |
| 94 | + }, |
| 95 | +}; |
| 96 | +``` |
| 97 | + |
| 98 | +Use the custom function you have defined: |
| 99 | + |
| 100 | +```css |
| 101 | +.foo { |
| 102 | + --shadow-color: blue; |
| 103 | + box-shadow: --shadow(); /* produces a blue shadow */ |
| 104 | + /* or just */ |
| 105 | + box-shadow: --shadow(blue); |
| 106 | +} |
| 107 | +``` |
| 108 | + |
| 109 | +will be processed to: |
| 110 | + |
| 111 | +```css |
| 112 | +.foo { |
| 113 | + --shadow-color: blue; |
| 114 | + box-shadow: 2px 2px var(--shadow-color, black); /* produces a blue shadow */ |
| 115 | + /* or just */ |
| 116 | + box-shadow: 2px 2px blue; |
| 117 | +} |
| 118 | +``` |
| 119 | + |
| 120 | +### Arguments validation |
| 121 | + |
| 122 | +You can validate functions arguments and output warnings if they are incorrect. |
| 123 | + |
| 124 | +```js |
| 125 | +function negative(value, ...rest) { |
| 126 | + if (!value) { |
| 127 | + throw new Error( |
| 128 | + `The --negative(…) function requires an argument, but received none.`, |
| 129 | + ); |
| 130 | + } |
| 131 | + |
| 132 | + if (rest.length > 0) { |
| 133 | + throw new Error( |
| 134 | + `The --negative(…) function only accepts a single argument, but received ${ |
| 135 | + rest.length + 1 |
| 136 | + }.`, |
| 137 | + ); |
| 138 | + } |
| 139 | + |
| 140 | + return `calc(-1 * ${value})`; |
| 141 | +} |
| 142 | + |
| 143 | +module.exports = { |
| 144 | + plugins: { |
| 145 | + '@yuheiy/postcss-custom-functions': { |
| 146 | + functions: { |
| 147 | + '--negative': (value, ...rest) => negative, |
| 148 | + }, |
| 149 | + }, |
| 150 | + }, |
| 151 | +}; |
| 152 | +``` |
| 153 | + |
| 154 | +This implementation is inspired by [Tailwind CSS’s `css-functions.js`](https://github.com/tailwindlabs/tailwindcss/blob/v4.0.0/packages/tailwindcss/src/css-functions.ts). |
| 155 | + |
| 156 | +### Fluid Typography |
| 157 | + |
| 158 | +You can also implement [Fluid Typography](https://www.smashingmagazine.com/2022/01/modern-fluid-typography-css-clamp/) as a custom function, using the [`tan(atan2())` technique](https://dev.to/janeori/css-type-casting-to-numeric-tanatan2-scalars-582j) to remove px units and calculate them in CSS. |
| 159 | + |
| 160 | +```js |
| 161 | +function fluid( |
| 162 | + minSize, |
| 163 | + maxSize, |
| 164 | + minBreakpoint = 'var(--breakpoint-sm)', |
| 165 | + maxBreakpoint = 'var(--breakpoint-xl)', |
| 166 | + ...rest |
| 167 | +) { |
| 168 | + if (!minSize || !maxSize) { |
| 169 | + throw new Error( |
| 170 | + 'The --fluid(…) function requires 2–4 arguments, but received none.', |
| 171 | + ); |
| 172 | + } |
| 173 | + |
| 174 | + if (rest.length > 0) { |
| 175 | + throw new Error( |
| 176 | + `The --fluid(…) function only accepts 4 arguments, but received ${ |
| 177 | + rest.length + 1 |
| 178 | + }.`, |
| 179 | + ); |
| 180 | + } |
| 181 | + |
| 182 | + const slope = `calc(tan(atan2(${maxSize} - ${minSize}, 1px)) / tan(atan2(${maxBreakpoint} - ${minBreakpoint}, 1px)))`; |
| 183 | + const intercept = `calc(tan(atan2(${minSize}, 1px)) - ${slope} * tan(atan2(${minBreakpoint}, 1px)))`; |
| 184 | + |
| 185 | + return `clamp(${[ |
| 186 | + `min(${minSize}, ${maxSize})`, |
| 187 | + `${slope} * 100lvi + ${intercept} / 16 * 1rem`, |
| 188 | + `max(${minSize}, ${maxSize})`, |
| 189 | + ].join(', ')})`; |
| 190 | +} |
| 191 | + |
| 192 | +module.exports = { |
| 193 | + plugins: { |
| 194 | + '@yuheiy/postcss-custom-functions': { |
| 195 | + functions: { |
| 196 | + '--fluid': fluid, |
| 197 | + }, |
| 198 | + }, |
| 199 | + }, |
| 200 | +}; |
| 201 | +``` |
| 202 | + |
| 203 | +Use the custom function you have defined: |
| 204 | + |
| 205 | +```css |
| 206 | +:root { |
| 207 | + --breakpoint-sm: 40rem; |
| 208 | + --breakpoint-md: 48rem; |
| 209 | + --breakpoint-lg: 64rem; |
| 210 | + --breakpoint-xl: 80rem; |
| 211 | + --breakpoint-2xl: 96rem; |
| 212 | +} |
| 213 | + |
| 214 | +h1 { |
| 215 | + font-size: --fluid(2rem, 4rem); |
| 216 | +} |
| 217 | +``` |
| 218 | + |
| 219 | +will be processed to: |
| 220 | + |
| 221 | +<!-- prettier-ignore --> |
| 222 | +```css |
| 223 | +:root { |
| 224 | + --breakpoint-sm: 40rem; |
| 225 | + --breakpoint-md: 48rem; |
| 226 | + --breakpoint-lg: 64rem; |
| 227 | + --breakpoint-xl: 80rem; |
| 228 | + --breakpoint-2xl: 96rem; |
| 229 | +} |
| 230 | + |
| 231 | +h1 { |
| 232 | + font-size: clamp(min(2rem, 4rem), calc(tan(atan2(4rem - 2rem, 1px)) / tan(atan2(var(--breakpoint-xl) - var(--breakpoint-sm), 1px))) * 100lvi + calc(tan(atan2(2rem, 1px)) - calc(tan(atan2(4rem - 2rem, 1px)) / tan(atan2(var(--breakpoint-xl) - var(--breakpoint-sm), 1px))) * tan(atan2(var(--breakpoint-sm), 1px))) / 16 * 1rem, max(2rem, 4rem));} |
| 233 | +``` |
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