js 生成 uuid

// 生成uuid

        generate_uuid: function(){

            var d = new Date().getTime();

            if(window.performance && typeof window.performance.now === "function"){

                d += performance.now(); //use high-precision timer if available

            }

            var uuid = 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {

                var r = (d + Math.random()*16)%16 | 0;

                d = Math.floor(d/16);

                return (c =='x' ? r : (r&0x3|0x8)).toString(16);

            });

            return uuid;

        },