Three implementations of `map` in continuation passing style.

cps-map.js

(function () {
    "use strict";

    var first = function (arr, c) {
        c(arr[0]);
    };

    var rest = function (arr, c) {
        c(arr.slice(1));
    };

    var append = function (arr, el, c) {
        c(arr.concat([el]));
    }

    var map1 = function (arr, f, c) {
        var helper = function (arr, newArr, f, c) {
            if (arr.length == 0) {
                c(newArr);
            } else {
                first(arr, function (oldFirst) {
                    rest(arr, function (r) {
                        f(oldFirst, function (newFirst) {
                            append(newArr, newFirst, function (newArr) {
                                helper(r, newArr, f, c);
                            });
                        });
                    });
                });
            }
        }

        helper(arr, [], f, c);
    };

    var prepend = function (el, arr, c) {
        c([el].concat(arr));
    }

    var map2 = function (arr, f, c) {
        if (arr.length == 0) {
            c([]);
        } else {
            rest(arr, function (r) {
                map2(r, f, function(newArr) {
                    first(arr, function (el) {
                        f(el, function (newEl) {
                            prepend(newEl, newArr, function (newArr) {
                                c(newArr);
                            });
                        });
                    });
                });
            });
        }
    };

    var deCons = function (arr, c) {
        first(arr, function (first) {
            rest(arr, function (rest) {
                c(first, rest);
            });
        });
    };

    var map3 = function (arr, f, c) {
        if (arr.length == 0) {
            c([]);
        } else {
            deCons(arr, function (first, rest) {
                map3(rest, f, function (newArr) {
                    f(first, function (el) {
                        prepend(el, newArr, function (newArr) {
                            c(newArr);
                        });
                    });
                });
            });
        }
    };

    var inc = function (i, c) {
        c(i + 1);
    };

    var arr = [1,2,3,4,5];

    map1(arr, inc, function (res) { console.log(res); });
    map2(arr, inc, function (res) { console.log(res); });
    map3(arr, inc, function (res) { console.log(res); });
})();