CanJS storing a todo to a file

I am writing a SPA using CanJS which has a list and user can add the list. I want to store the newly added item permanently by writing it to a file. Can some one help me?

'.btn_save click': function (ele, ev) {
        var self = this;
        var val = this.$input.val();
        // get the currently selected model
        var model = this.state.attr('selected');
        // store if it is new
        var isNew = model.isNew();
        // update the attributes
        model.attr('name', val);
        // save it
        model.save(function (library) {
            if (isNew) {
                // if new then append it to the list
                self.libraries.push(library);
            }

            self.resetSelected();
        });
        return false;
    },

This saves the item temporarily for the current browsing session. I want to store it permanantly.

You can save your list localy to a file using HTML5 FileWriter API. See this question. Unless using HTML5, it's not possible to save file using javascript on user's computer.