code: function(nodePath, state) {
          var replacements = [];
          var expr = getGlobalExpression(state, getFilenameNoExt(state.file.opts.filename));
          var expression = nodePath.node.declaration;
          if (expression.id &&
            (t.isFunctionDeclaration(expression) || t.isClassDeclaration(expression))) {
            replacements.push(expression);
            expression = expression.id;
          }
          assignToGlobal(expr, replacements, expression);
          nodePath.replaceWithMultiple(replacements);
        }
docs: Replaces default export declarations with assignments to global variables.
  @param {!NodePath} nodePath
  @param {!Object} state