javascript - What exactly are expressions that produce *side effects*? -


i have trouble understanding paragraph in page https://developer.mozilla.org/en/javascript/reference/operators/special/void:

this operator allows inserting expressions produce side effects places expression evaluates undefined desired.

what expressions produce side effects ?

a function 2 things typically: perform something , return value. functions 1 of things, both. instance function:

function square(x) {   return x * x; }

is side-effect free since return value , invocation can replaced return value. on other hand, alert() called side-effects (alerting user) , never return value.

so void operator makes javascript ignore return value , state you're interested function's side-effects.


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