the other answers are entirely correct if your string has only 1 space between words.
if you have multiple spaces between words, then things are a bit different:
to get just the words, in reverse order, rejoined by 1 space:
str.split(/s+/).reverse().join(" ")
to reverse the entire string, and still have the original whitespace:
str.split(//).reverse().join('')
the first one uses a regex, "/s+/", to match an entire run of spaces, instead of a single space. it rejoins the words with a single space.
the second one uses a regex, "//", to just split on the boundaries between words and non-words. since the runs of spaces will be preserved, it just rejoins with an empty string.
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