I thought this was working at some point, but it doesn't seem to now. FOO() returns undefined in JS, when it should return 123:

(defun bar (fn)
  (funcall fn))

(defun foo ()
  (bar (lambda () (return-from foo 123))))

It seems the value stored under the name "ps-return-value" isn't actually returned:

function foo() {
    try {
        return bar(function () {
            throw { 'ps-block-tag' : 'foo', 'ps-return-value' : 123 };
        });
    } catch (err) {
        if (err && 'foo' === err['ps-block-tag']) {
            err['ps-return-value'];
        } else {
            throw err;
        };
    };
};