JavaScript test to see if browser supports flexbox

supports-flex.js

// via Ethan Marcotte (10 December 2015)
// https://24ways.org/2015/putting-my-patterns-through-their-paces/
// If the browser passes the test, then a class of supports-flex gets applied to our html element. 

var doc = document.body || document.documentElement;
var style = doc.style;

if ( style.webkitFlexWrap == '' ||
    style.msFlexWrap == '' ||
    style.flexWrap == '' ) {
  doc.className += " supports-flex";
}