Sequelize update

According to the documentation the update method takes two parameters - first one is values which will be used to perform the update, and second one is options - so in your case this is the where clause. If you want to perform an update on a single instance only, you can do it in two ways - use Model.update() method, which can update multiple instances of this model at once matching the where clause, or perform instance.update() in order to update only the single instance. First option will look like that:

let updateValues = { name: 'changed name' };
models.Model.update(updateValues, { where: { id: 1 } }).then((result) => {
    // here your result is simply an array with number of affected rows
    console.log(result);
    // [ 1 ]
});

The first option is not very useful when you want to update only single instance. So that is why there is a possibility of performing update() on Sequelize model instance

let updateValues = { name: 'changed name' };
instance.update(updateValues).then((self) => {
    // here self is your instance, but updated
});

---

In your case, if the item parameter is a Sequelize model instance (not a plain javascript JSON object), your update function could be like that

exports.updateItem = function(item){
    return item.update(values).then((self) => {
        return self;
    }).catch(e => {
        console.log(e);
    });
};

However, if the item is not a sequelize model instance but only a plain object with values you want to update, it could be done in two ways - first is to use Model.update() (just like you did), or second one is to retrieve TimesheetItem with id = item.id and then perform instance.update() as shown above

exports.updateItem = function(item){
    models.TimesheetItem.update(item, { where: { id: item.id } }).then((result) => {
        // here result will be [ 1 ], if the id column is unique in your table
        // the problem is that you can't return updated instance, you would have to retrieve it from database once again
        return result;
    }).catch(e => {
        console.log(e);
    });
};

Or the second option with returning instance and performing update on it

exports.updateItem = function(item) {
    return models.TimesheetItem.findById(item.id).then((itemInstance) => {
        return itemIstance.update(item).then((self) => {
            return self;
        });
    }).catch(e => {
        console.log(e);
    });
}

The difference is that you do not need to create and return your own Promise - sequelize methods like update() return promises by themselves.