1.回调函数
function timer(time, callback){
setTimeout(function(){
callback();
}, time);
}
timer(3000, function(){
console.log(123);
})
timer()
async function testResult() {
let first = await doubleAfter2seconds(30);
let second = await doubleAfter2seconds(50);
let third = await doubleAfter2seconds(30);
console.log(first + second + third);
}
