如何正确地称这个承诺链

我使用以下代码与blueBird lib,但在控制台我得到错误:

未捕获的TypeError:无法读取未定义的属性'then'

我在那时([SUCESS])没有看到console.log 为什么？

我有两个文件1.index.html,代码如下

和script.js使用以下代码

var stepOne = new Promise(function (resolve, reject) {
    setTimeout(function () {
        console.log("Step 1 -->Successfully Resolving");
        resolve();
    }, 5000);
    setTimeout(function () {
        console.log("Step 1 -->First timeout, rejecting the promise");
        reject();
    }, 2000);
}).catch(function () {
        console.log("Step 1 -->Timed out 1 ... retrying");
    });


var stepTwo = new Promise(function (resolve, reject) {
    setTimeout(function () {
        console.log("Step 2 -->Successfully Resolving Step two");
        resolve();
    }, 5000);
    setTimeout(function () {
        console.log("Step 2 -->First timeout, rejecting the promise");
        reject();
    }, 2000);
}).catch(function () {
        console.log("Step 2 -->timed out 2 ... retrying");
    });


stepOne.then(function () {
    console.log("[SUCCESS] Step 1");
}).stepTwo.then(function () {
        console.log("[Success] Step 2");
    })

const step1 = () => new Promise(...); // Step 1 code in this promise
const step2 = () => new Promise(...); // Step 2 code in this promise

// By this point, nothing runs, we only defined functions.

step1() // Run step one
  .then(() => console.log('[SUCCESS] Step 1');
  .then(step2); // Run step two
  .then(() => console.log('[SUCCESS] Step 2');