关于javascript事件循环的一些题

// 测试代码
console.log('main1');
// 该函数仅在 Node.js 环境下可以使用
process.nextTick(function(){
    console.log('process.nextTick1');
});
setTimeout(function(){
    console.log('setTimeout');
    process.nextTick(function(){
        console.log('process.nextTick2');
    });
},0);
newPromise(function(resolve,reject){
    console.log('promise');
    resolve();
}).then(function(){
    console.log('promise then');
});
console.log('main2');


// 执行结果
main1
promise
main2
process.nextTick1
promise then
setTimeout
process.nextTick2

function  foo(){
    console.log("Start of queue");
    bar();
    setTimeout(function(){
        console.log("Middle of queue");
    },0);
    Promise.resolve().then(function(){
        console.log("Promise resolved");
        Promise.resolve().then(function(){
            console.log("Promise resolved again");
        });
    });
   console.log("End of queue");
}

function bar(){
    setTimeout(function(){
          console.log("Start of next queue");
    },0);
    setTimeout(function(){
          console.log("End of next queue");
    },0);
}

foo();

// 输出

Start of queue
Endof queue
Promise resolved
Promise resolved again
Start of next queue
Endof next queue
Middle of queue

Promise.then 是异步执行的，而创建 Promise 实例 （executor） 是同步执行的