Is a function that calls Math.random() pure?

Question

Is the following a pure function?

function test(min,max) {
   return  Math.random() * (max - min) + min;
}

My understanding is that a pure func

Answer 1

From mathematical point of view, your signature is not

test:  -> 

but

test:  -> 

where the environment is capable of providing results of Math.random(). And actually generating the random value mutates the environment as a side effect, so you also return a new environment, which is not equal to the first one!

In other words, if you need any kind of input that does not come from initial arguments (the part), then you need to be provided with execution environment (that in this example provides state for Math). The same applies to other things mentioned by other answers, like I/O or such.

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As an analogy, you can also notice this is how object-oriented programming can be represented - if we say, e.g.

SomeClass something
T result = something.foo(x, y)

then actually we are using

foo:  -> 

with the object that has its method invoked being part of the environment. And why the SomeClass part of result? Because something's state could have changed as well!