[Cordova] inappbrowser Cannot read property 'open' of undefined

document.addEventListener("deviceready", onDeviceReady, false);
function onDeviceReady() {
  window.open = cordova.InAppBrowser.open;
  var ref2 = cordova.InAppBrowser.open(encodeURI('http://ja.m.wikipedia.org/wiki/ハングル'), '_blank', 'location=yes');
}

inappbrowser Cannot read property 'open' of undefined

you have to write the code in document.addEventListener ... ! 

reference : https://stackoverflow.com/questions/37439043/cordova-inapp-browser-throws-error