Providing It was syntactically correct the first call would assign e to a variable b for each iteration ( pretty pointless )
The arr.map providing you had a variable on the left side would output the result of each iteration into said array ( so an array containing all b values - however I guess you meant arr.map(e => e)
Providing arr is iterable (e.g. an array) it's perfectly valid js. Your linter might scream at you to add braces and a semicolon, but neither is needed for correctness here.
