modernizr/feature-detects/css/calc.js

Modernizr is a JavaScript library that detects HTML5 and CSS3 features in the user’s browser.

/*!
{
  "name": "CSS Calc",
  "property": "csscalc",
  "caniuse": "calc",
  "tags": ["css"],
  "authors": ["@calvein"]
}
!*//* DOC

Method of allowing calculated values for length units. For example:

```css
#elem {
  width: calc(100% - 3em);
}
```

*/
define(['Modernizr', 'createElement', 'prefixes'], function( Modernizr, createElement, prefixes ) {
  Modernizr.addTest('csscalc', function() {
    var prop = 'width:';
    var value = 'calc(10px);';
    var el = createElement('div');

    el.style.cssText = prop + prefixes.join(value + prop);

    return !!el.style.length;
  });
});