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https://github.com/ahrefs/bs-emotion

BuckleScript bindings to Emotion
https://github.com/ahrefs/bs-emotion

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BuckleScript bindings to Emotion

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# bs-emotion



> **Warning**

> This repository is no longer maintained, as we don't use it anymore at Ahrefs. For alternatives, check [styled-ppx](https://github.com/davesnx/styled-ppx/) or [bs-css](https://github.com/giraud/bs-css).



bs-emotion status

bs-emotion-ppx status



BuckleScript bindings to [Emotion](https://emotion.sh).



## BuckleScript v8+



`bs-emotion` and `bs-emotion-ppx` are compatible with BuckleScript v7 starting from version 2.0.0.



## Previous versions



Use v1.0.1 if you need compatibility with BuckleScript v7.



If you need to use them with BuckleScript v5 or below, install the earlier versions:

- `@ahrefs/bs-emotion` version ^0.1.2

- `@ahrefs/bs-emotion-ppx` version ^0.0.7



## Installation

Get the package:



```shell

# yarn

yarn add @ahrefs/bs-emotion

# or npm

npm install --save @ahrefs/bs-emotion

```



Then add it to `bsconfig.json`:



```json

"bs-dependencies": [

  "@ahrefs/bs-emotion"

]

```



### `bs-emotion-ppx`

If you want to auto-label generated classnames for easier debugging, you can install `bs-emotion-ppx`:



```shell

# yarn

yarn add --dev @ahrefs/bs-emotion-ppx

# or npm

npm install --save-dev @ahrefs/bs-emotion-ppx

```



Then add it to `bsconfig.json`:



```json

"ppx-flags": ["@ahrefs/bs-emotion-ppx/ppx -as-ppx"],

```



## Usage

### Defining styles

There are 2 ways to define a CSS class:



```ocaml

open Emotion



(* If you use ppx *)

let button = [%css [ ... ]] (* -> "css-HASHED-button" *)



(* If you don't use ppx *)

let button = css [ ... ] (* -> "css-HASHED" *)

```



And here's real-world example:

> It's in OCaml syntax, but you can use Reason too.



```ocaml

(* ComponentStyles.ml *)



open Emotion



let container = [%css [

  display `flex;

  flexFlow `column `nowrap;

  alignItems `center;

]]



let shape = [%css [

  display `flex;

  flexFlow `row `nowrap;

  alignItems `center;

  justifyContent `center;

  transitionProperty "border-radius";

  transitionDuration (`ms 100);

  transitionTimingFunction `easeInOut;

  width (`px 200);

  height (`px 200);

  borderRadius (`px 6);

  backgroundColor (`hex "29d");



  (* :hover selector, same as `select ":hover" [ ... ]` *)

  hover [

    borderRadius (`pct 50.);

    important (cursor `grab);

  ];

]]



(* Dynamic styling *)

(* NOTE: ppx supports functions with max 2 arguments *)

let text ~size = [%css [

  color (`hex "fff");

  fontSize (`px size);

  fontWeight 700;



  (* Transition takes property, duration, timing-function & delay *)

  transition "font-size" (`ms 100) `easeInOut `zero;



  (* You can define multiple transitions by packing them into list of tuples *)

  transitions [

    ("font-size", `ms 100, `easeInOut, `ms 0);

  ];



  (* Complex selector that uses .container class defined above *)

  (* Rendered as: `.container:hover .text {...}` *)

  select {j|.$container:hover &|j} [

    fontSize Calc.(((`px size) + (`pct 150.)) * (`n 1.5));

  ];



  (* @media quiery with nested selectors *)

  media "(max-width: 900px)" [

    color (`hex "ff69b4");



    select ":hover" [

      color (`hex "fff");

    ];

  ];

]]



(* Define keyframes *)

let bounce = keyframes [

  (0,   [ transform (`translateY `zero); ]);

  (50,  [ transform (`translateY (`px (-20))); ]);

  (100, [ transform (`translateY `zero); ]);

]



let animated = [%css [

  (* Use generated animation name *)

  animationName bounce;

  animationDuration (`ms 300);

  animationIterationCount (`i 7);

]]



(* Compose things *)

let smallText = [%css [

  fontSize (`em 0.8);

]]



let note = css ~extend: smallText [

  label "note";



  marginTop (`px 10);

]

```



### Applying styles

```reason

/* Component.re */



module Css = ComponentStyles;



let component = ReasonReact.statelessComponent(__MODULE__);



let make = _ => {

  ...component,

  render: _ => 
 ... 
,

};

```



### Composing classnames



#### Cx

This package provides `Cx.merge` function which is a binding to Emotion's [`cx`](https://emotion.sh/docs/cx). It merges 2 Emotion's CSS classes into single unique class. See the [Caveats](#caveats) section for details.



#### Cn

Also, there is [`re-classnames`](https://github.com/alexfedoseev/re-classnames). You can use it to combine classnames together. It's not aware of Emotion and simply operates on strings.



#### Caveats

First, let's talk about the difference between `Cn.make` and `Cx.merge`:



```reason

Cn.make([Css.one, Css.two]) /* => "css--one css--two" */

Cx.merge([|Css.one, Css.two|]) /* => "css--one-two" */

```



If the former simply concatenates two classname strings into a single string (and as a result 2 CSS classes are applied) then the latter merges 2 Emotion classes into single unique class and applies it to a node (as a result 1 unique CSS class is applied).



##### Caveat #1



```reason



  



```



```ocaml

let foo = css [ ... ]

let bar = css [ ... ]



let button = css [

  ...



  select {j|.$foo:hover &|j} [

    (*

      It won't work due to `.foo` class is being merged w/ `.bar`

      into single unique classname inside component

    *)

  ]

]

```



To make this css work you can use `Cn.make`, e.g:



```reason



```



##### Caveat #2



```reason

let make = (~className, children) => {

  ...component,

  render: _ =>

    


      ...children

    
,

};

```



Oftentimes, UI abstractions accept `className` prop to extend or override default CSS of abstraction. Since position of classname on application site doesn't guarantee precedence of `className` prop (in CSS, precedence is determined by position of classname on definition site), it's not safe to use `Cn.make` here. In this case, use `Cx.merge` since `Emotion` determines precedence on application site and guarantees that last classname has precedence over the preceding classes.



```reason



```



## Contributing



See [`CONTRIBUTING.md`](./CONTRIBUTING.md).



## Thanks

- [`glennsl/bs-typed-css-core`](https://github.com/glennsl/bs-typed-css-core) and [`SentiaAnalytics/bs-css`](https://github.com/SentiaAnalytics/bs-css) for examples and inspiration.