process.nextTick()与promise.then()

Question

process.nextTick(function(){

    console.log(7);

});

new Promise(function(resolve){

    console.log(3);

    resolve();

    console.log(4);

}).then(function(){

    console.log(5);

});

process.nextTick(function(){

    console.log(8);

});

这段代码运行结果是3，4，7，8，5

process.nextTick和Promise都是Microtasks，为什么process.nextTick会先执行？