關(guān)于 promise 和 setTimeout

var p1 = new Promise(function (resolve, reject) {
    setTimeout(function(){
        resolve(1);
        console.log('p1');
    },5000)
});

var p2 = new Promise(function (resolve, reject) {
      resolve(p1);
}).then(function(data){
    console.log(data);
    console.log('p2');
})

為什么結(jié)果是p1==>1==>p2，而不是1==>p2==>p1？