activate-deactivate for header

gistfile1.js

activate() {
 //read model for application header
  var appModel = this.modelFor(`application`);
 //get current header that is rendered before we enter current route
  var currentHeader = appModel.get(`currentHeader`);
  //save that header to our current route
  this.set(`prevHeader`) = currentHeader;
//set current app header to one that is defined in current route
  appModel.set(‘currentHeader’) = this.get(`header`); 
  
  this._super(…arguments);
}

deactivate() {
    //read model for application header
  var appModel = this.modelFor(`application`);
  //restore old header before we exit
  appModel.set(`currentHeader`,  this.set(`prevHeader`));
  
   this._super(…arguments);
}