user.schema.ts

var MutationUpdate = {
  type: new GraphQLList(UserType),
  description: 'Update a User',
  args: {
    id: {
      name: 'User id',
      type: new GraphQLNonNull(GraphQLFloat)
    },
    newName: {
      name: 'New user name',
      type: new GraphQLNonNull(GraphQLString)
    }
  },
  resolve: (root, {id, newName}) => {
    var selectedUser = USERs.filter(function(user) {
      return user.id === id;
    })[0];
    selectedUser.name = newName;
   return USERs;
  }
};