_gaq.push() is not a function

if (typeof _gaq === 'undefined' || typeof _gaq !== 'object') { 
  var _gaq = {}; 
  _gaq.push =  function(array){
    if(array[0] === '_trackPageview'){
       dataLayer.push({
        'event': 'pageview',
        'pagePath': array[1] 
      });
    }else if(array[0] === '_trackEvent'){
      dataLayer.push({
        'event': 'event',
        'category': array[1],
        'action': array[2], 
        'label': array[3], 
        'value': array[4] 
      });
    }
  }
}