Originally posted on my blog
JavaScript array methods enable us to manipulate our data. However, we've to use them with care depending on how they...
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I think forEach is incorrectly categorized as a mutator function, since it does not modify the array itself, it only might modify the state of the objects inside the array. Actually, most of the non-mutator functions can also modify the state of the objects, for example map and filter.
ForEach itself does not mutate the array. But the function passed as parameter can mutate the array. And mostly forEach is used with a function parameter therefore it's more a mutator than a non-mutator. For the others,
mapandfilterthey both return a new array andreducereturn a single value. But overall they does not mutate the original array.can you give me an example where
forEach()changes the original Array completely?You pass a function to map and filter as well, so they are also able to change the state of the object. Obviously, it's a bad practice to do so but still possible.
You have to reassign e.g. arr = arr.map(x=>x**x), since arr.map(x=>x*x) won't change arr itself, it is new array, same as .filter.
Nice overview. But yes, I would not say .forEach() mutates too, since it is just kind of loop function - passed function may or may not mutate array on which it runs, it could be used for some side effects, it could be used to modify totally different array/object - it is just a loop over items in array and it does not imply any kind of function / computation in that loop.