fetch meta attribute in vanilla js (with og support)

gistfile1.js

/**
 * Fetches a meta (+ open graph) attribute from HTML
 *
 * @returns value The request content of the meta tag (nullable)
 */
var getMetaAttribute = function( attribute )
{
  var key = null;
  var value = null;
  var meta = document.getElementsByTagName('meta');

  // search desired tag
  for( var i = 0, l = meta.length; i < l; i += 1 )
  {
    key = meta[i].name || meta[i].getAttribute('property');

    if( !key )
    {
      continue;
    }

    // found an open graph tag
    if( key.split(':')[0] === 'og' )
    {
      key = key.split(':')[1];
    }

    // is this the tag we want?
    if( key === attribute )
    {
      value = meta[i].content;
    }
  }

  return value;
}