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    For anyone interested, I wrote a lens library for JavaScript a few days ago:

    https://github.com/puffnfresh/fantasy-lenses

    The first example can be written like so:

    var locationX = location.andThen(x);
    locationX.set(locationX.get() + 10);
    
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      Michael Greenberg also published a JavaScript lenses library back in 2007, as part of his thesis at the University of Pennsylvania:

      http://www.cis.upenn.edu/~mgree/ugrad/lenses/docs/overview-summary-lens.js.html

      It’s a bit dated now, to be sure, as there have since been many developments in the field of “bidirectional programming”. See, for example, Daniel Wagner’s paper on “Edit Lenses”:

      http://dmwit.com/papers/201107EL.pdf