SOURCE

//函数参数默认值
function log(x , y = 5){
    console.log(x,y)
}


var async1 = async function () {
   console.log('async1 start');
   await async2();
    console.log('async1 end');

};
var async2 = async function(){
    console.log('async2');
}

setTimeout(function(){
    console.log('async3');
},0);

async1();