aspect-ratio.js

/*

# Aspect Ratio Mixin for reproCSS
## version 0.0.10

Define a height for HTML elements based on the element's width and a supplied aspect ratio.

### Syntax

    aspectRatio(selector, ratio)

- `selector` is a CSS selector
- `ratio` is a ratio expressed as `width/height` or a number

### Example

    aspectRatio('iframe', 16/9)

- https://github.com/tomhodgins/reprocss

Author: Tommy Hodgins

License: MIT

*/

function aspectRatio(selector, ratio) {

  var tag = document.querySelectorAll(selector)
  var style = ''
  var count = 0

  for (var i=0; i < tag.length; i++) {

    var attr = selector.replace(/\W+/g, '')

    tag[i].setAttribute('data-aspect-ratio-' + attr, count)

    style += '\n/* ' + selector + ' { aspect-ratio: ' + ratio + '; } */\n'
             + '[data-aspect-ratio-' + attr + '="' + count + '"] {\n'
             + '  height: ' + (tag[i].offsetWidth / ratio) + 'px;\n'
             + '}\n'

    count++

  }

  return style

}