As we know a pure function doesn't depend on and doesn't modify the states of variables out of its scope. I have a clarity on these that if a function is dependent on some arguments it becomes non pure function but why is Date.now() or Math.random() called non pure function. Can someone explain me the basics behind it?
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Steffen Moritz
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Tanveer
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Where did you get these definitions from, and who told you / where do you read that Date.now() & Math.random() are not so called "pure" functions? – ControlAltDel Jun 26 '19 at 18:22
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@ControlAltDel https://en.wikipedia.org/wiki/Pure_function `Date.now()` and `Math.random()` are definitionally not pure. – lux Jun 26 '19 at 18:38
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Related: https://stackoverflow.com/questions/37244023 . – atravers Jan 13 '22 at 01:38
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Pure functions:
- Do not depend on or modify external state
- Return the same result every time for the same input
Both functions you mention violate #2 - they return different value everytime you call them. In reality they also violate #1 since they are accessing and/or modifying global state to do their work.
Brandon
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Your definition is incomplete, let's see e.g. https://en.wikipedia.org/wiki/Pure_function
a function that has the following properties:
- Its return value is the same for the same arguments
- Its evaluation has no side effects
Neither Date.now() nor Math.random() meet the 1st point of the definition, so they are not pure functions.
