Can you give examples of methods that are idempotent?

Idempotence means that multiple executions of a method with the same input data will not change the system's state after the first call.

Examples of idempotent methods in Node.js:

• HTTP methods GET, PUT, DELETE are considered idempotent by default.
• A method that updates a record in a database to set a specific value, for example:

app.put('/user/:id', (req, res) => {
  // Update user with id
  User.updateOne({ _id: req.params.id }, { name: req.body.name })
    .then(() => res.send('Updated'));
});

• Resource deletion method:

app.delete('/item/:id', (req, res) => {
  Item.deleteOne({ _id: req.params.id })
    .then(() => res.send('Deleted'));
});

Repeated calls to PUT or DELETE with the same parameters will not change the state after the first successful call, which is the essence of idempotence.