[Vuejs]-Initialize VueJs after opening new tab

When you specify a selector for your el, Vue will look in the current document for it. The new tab will not be part of the current document.

Save a reference when you open the tab. Write the HTML into its document. Query the #app out of the document, and use the actual element instead of a selector in your Vue setup:

var vm = new Vue({
  el: newWindow.document.getElementById('app')
});