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(...Array([random number]).keys().toString()) why the length and values of this expression always gives the same result?

In Javascript, using spread operator we can iteration an Array.

[...Array(5).keys()] this gives a result ->

[0,1,2,3,4]

when I try to convert these number to a string

[...Array(5).keys().toString()] this gives a result ->

["[", "o", "b", "j", "e", "c", "t", " ", "A", "r", "r", "a", "y", " ", "I", "t", "e", "r", "a", "t", "o", "r", "]"]

[...Array(10).keys().toString()] this also gives a same result as above.

Why is this happening?

Solution

  • Array(5).keys() is an Array Iterator. When you do

    [...Array(5).keys().toString()]

    you are not converting the keys to string, but you are trying to convert the iterator to String which gives you "[object Array Iterator]" as a character array.

    You need to do:

    [...Array(5).keys()].map(k => k.toString())

    to convert all keys to String