JavaScript is a minefield of unexpected behavior when you try things like this. Besides the issue with this-binding already mentioned in the thread, there are other examples of weird stuff that happens when you don't introduce an apparently redundant lambda:

    > ['10', '10', '10', '10', '10'].map(parseInt)
    [ 10, NaN, 2, 3, 4 ]

    > ['10', '10', '10', '10', '10'].map(x => parseInt(x))
    [ 10, 10, 10, 10, 10 ]