gos1-b6.js

// Approach 1
function getMapping(){
  const tagMap = {};
  this.selectedTags.forEach(( tag, index ) => {
    if ( tag !== undefined ) {
      tagMap[ tag ] = this.headers[ index ];
    }
  } )
  return tagMap;
}

// Approach 2
function getMapping(){
  return this.selectedTags
    .filter( tag => tag !== undefined )
    .reduce(( map, tag, index ) => map[ tag ] = this.headers[ index ], {} );
}