code: function findUnusedVariableDeclarators (ast) {
    var unused = [];
    traverse.traverse(ast, {
      enter: function (node, parent) {
        var scope, refs;
        if (node.type === 'VariableDeclarator' && (scope = findScope(ast, node))) {
          refs = fast.filter(findVariableReferences(scope, node.id), function (item) {
            return item !== node.id;
          });
  
          if (!refs.length) {
            unused.push(node);
          }
        }
      }
    });
    return unused;
  }
docs: Find declarators of unused variables.