生成uuid唯一标识符

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;
},