[Javascript] Autocomplete Textarea from localStorage

AutocompleteTextarea

var AutocompleteTextarea = function () {
    this.lastFocus = {};
};


AutocompleteTextarea.prototype = (function () {

    function setSave(textareaId, storageKey) {
        $("form").on("submit", function (ev) {

            var value = $("#" + textareaId).val();

            if (!storageKey) return;
            if (!value) return;

            var storageData = null;
            if (window.localStorage[storageKey]) {
                try {
                    storageData = JSON.parse(window.localStorage[storageKey]);
                } catch (e) {
                    window.localStorage.removeItem(storageKey);
                }
            }

            if (!storageData) storageData = [];

            var newStorage = [value],
                currentValue,
                i = 0;
            while (newStorage.length <= 5 && (currentValue = storageData[i++])) {
                if (currentValue != value) {
                    newStorage.push(currentValue);
                }
            }

            window.localStorage[storageKey] = JSON.stringify(newStorage);

        });
    }

    var initAutocomplete = function (textareaId) {
        var that = this;
        if (!textareaId) return;
        if (!window.localStorage) return;

        var storageKey = "autocompleteTextarea" + textareaId;
        setSave(textareaId, storageKey);

        if (!window.localStorage[storageKey]) return;

        var storageData = null;
        try {
            storageData = JSON.parse(window.localStorage[storageKey]);
        } catch (e) {
            window.localStorage.removeItem(storageKey);
        }

        if (storageData == null) return;

        $("#" + textareaId)
            .autocomplete({
                source: storageData,
                minLength: 0,
                autoFocus: true
            })
            .on("keydown", function (ev) {
                var $this = $(this);
                var val = $this.val();
                if (val == "" && ev.keyCode == 40) {
                    $this.autocomplete('search', val);
                }
            })
            .on("focus", function () {
                that.lastFocus[this.id] = 1;
            })
            .on("blur", function () {
                that.lastFocus[this.id] = -1;
            })
            .on("click", function (ev) {
                var $this = $(this);
                var val = $this.val();

                if (that.lastFocus[this.id] % 2 == 0) {
                    $this.autocomplete('search', val);
                } else {
                    $this.autocomplete('close');
                }

                that.lastFocus[this.id]++;

            });
    };


    return { initFor: initAutocomplete };
})();