Permission control with KnockoutJs

gistfile1.js

function Permissions(){
    var self = this;

    /*  Permissions */
    self.permissions = ko.observableArray([]);

     /*
     * Set Permission
     * @param{String} key
     * @param{boolean} value
     * @return{boolean}
     * Requirements: Underscore Js
     * Sample: self.set_permission('dashboard_statistics', true); --> bool
    */
    self.setPermission = function(key, value){
        var check = _.where(self.permissions(), {Key:key});
        if(check.length == 0 && typeof value == "boolean"){
            self.permissions.push({Key:key, Value:value});
            return true;
        }else{
            return false;
        }
    };

    /*
     * Check Permission
     * @param{String} key
     * @return{boolean}
     * Requirements: Underscore Js
     * Sample: self.has_permission('dashboard_statistics'); --> bool
    */
    self.hasPermission = function(key){
        var result = _.where(self.permissions(), {Key:key});
        if(result.length > 0){
            return result[0].Value;
        }else{
            return false;
        }
    };
}

gistfile2.js

function Persons(){
    this.permissions = new Permissions()
}

var person = new Persons();
person.permissions.setPermission('create_user', true);
person.permissions.setPermission('edit_user', false);

person.permissions.hasPermission('create_user') // true
person.permissions.hasPermission('edit_user') // false

// HTML: <span data-bind="visible: $root.permissions.hasPermission('create_user')">Create User </span>