promise 执行顺序

Question

console.log('main-1')function foo(param){  var p = new Promise(function(resolve, reject) {    console.log('promise-1')    if (param === 1) {       resolve('1')     } else {       reject('2')     }    console.log('promise-2')   })  return p }console.log('main-2') foo(1).then(function(value) {  console.log('then-1') })console.log('main-3')

Answer 1

运行结果是 main-1
main-2
promise-1
promise-2
main-3
then-1

为什么main-3 会在promise运行之后