# Compare two lists with DIFFARR: what to add, update and remove

> Use DIFFARR() to compare the items saved in the database with the items of a form and get the ones to add, to update and to remove.

Framework: total5
Product: Total.js 5 (total5@0.0.19)
Language: en
Content-SHA256: a12236697023df4617897c5ec8a240897c9b3ae8fe6c8ec55b1717c1d1f9bdaf
Snapshot: c0700e321579725c5cf4f5ace1ad7d2866d1b4f93c24a63c0b41b6b7998e976c
Sources: total5-installed@total5@0.0.19
Review: not-recorded

`DIFFARR(property, saved, submitted)` compares two arrays of objects by one property and returns an object with three lists:

- `add`: the objects of `submitted` whose property is **not** in `saved`
- `upd`: for the objects that are in both, `{ db, form }` with the saved object and the submitted one
- `rem`: the **values of the property** (not the objects) of the items of `saved` that are not in `submitted`

It is the usual step of saving an editable list: the form sends the whole list and you need to know what was created, what changed and what was deleted. The values are compared with `==`, so `1` and `'1'` are the same item.

```js controllers/lists.js
const saved = [
	{ id: 1, name: 'Book' },
	{ id: 2, name: 'Pen' },
	{ id: 3, name: 'Lamp' }
];

exports.install = function() {
	ROUTE('POST /sync/', sync);
};

function sync($) {
	const diff = DIFFARR('id', saved, $.body.items);
	$.json({
		add: diff.add,
		update: diff.upd.map(n => ({ id: n.db.id, from: n.db.name, to: n.form.name })),
		remove: diff.rem
	});
}
```