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54 lines
816 B
Markdown
54 lines
816 B
Markdown
---
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date: 2020-11-26
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id: 48609306-f2e9-4d01-b774-7d3ec34703aa
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title: idempotent
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---
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# Origin
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Idem is latin for 'same'.
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# Definition
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An operation or function, that when called multiple times will always
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produce the same result.
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# Examples
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## Idempotent
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``` javascript
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console.log(1 * 1 * 1 * 1)
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```
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``` javascript
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const set = new Set()
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set.add('blaat')
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set.add('blaat')
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set.add('blaat')
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console.log(set) // { 'blaat' }
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```
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### Practial examples
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- Get, Put & Delete endpoints on a REST api
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- Payment operations. Reposting the same form should not result in
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multiple charges to the customer.
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## Non idempotent
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``` javascript
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console.log(2 * 2 * 2 * 2)
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```
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``` javascript
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const arr = []
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arr.push('blaat')
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arr.push('blaat')
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arr.push('blaat')
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console.log(arr) // [ 'blaat', 'blaat', 'blaat' ]
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```
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