The grouping of expressions is clearer to many readers in the JS example. Unless you've spent a decent amount of time grokking the lambda calculus, the second line could be any of:

    (λx. (λf. f)) x
    (λx. (λf. f) x)
    (λx. (λf. f x))

The lambda calculus notation is weird. Using "." to separate parameter and body is unusual. The scope of the body isn't obvious.

JS is painfully verbose, but it's a verbose syntax many people have already put the time in to internalize.