`Object.assign` for browsers that don't support it

mixin.js

function mixin(target, source) {
  var from;
  var to = target;
  var index = 0;
  var total = arguments.length;
  var hasOwnProperty = Object.prototype.hasOwnProperty;

  while(++index < total){
    from = arguments[index];

    if (from != null) {
      for(var key in from) {
        if (hasOwnProperty.call(from, key)) {
          to[key] = from[key];
        }
      }
    }
  }

  return to;
}