What this snippet does
flat(1) flattens one level deep; flatMap is map then flat(1) — useful for one-to-many transformations.
Expected output
[ 1, 2, 3, 4, [ 5, 6 ] ] [ 1, 2, 3, 4, 5, 6 ] [ 'hello', 'world', 'foo', 'bar' ]
Why practise typing this
Typing arrays code builds muscle memory for the symbols and indentation JavaScript uses most, which prose-based typing tests never cover. DevType measures your words per minute and accuracy on this snippet and tracks the individual characters you mistype, so later lessons can target them.
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