Origin

Idem is latin for 'same'.

Definition

An operation or function, that when called multiple times will always produce the same result.

Examples

Idempotent [idempotent-1]

console.log(1 * 1 * 1 * 1)

const set = new Set()

set.add("blaat")
set.add("blaat")
set.add("blaat")

console.log(set) // { 'blaat' }

Practial examples

• Get, Put & Delete endpoints on a REST api
• Payment operations. Reposting the same form should not result in multiple charges to the customer.

Non idempotent

console.log(2 * 2 * 2 * 2)

const arr = []

arr.push("blaat")
arr.push("blaat")
arr.push("blaat")

console.log(arr) // [ 'blaat', 'blaat', 'blaat' ]