ES6 promise对象解决嵌套回调的问题

//promise
let state=1;
function step1(resolve,reject){
    console.log('1.开始洗菜做饭');
    if(state=1){
        resolve('洗菜做饭完成')
    }else{
        reject('洗菜做饭错误');
    }
}
function step2(resolve,reject){
    console.log('2.开始坐下来吃饭');
    if(state=1){
        resolve('坐下来吃饭完成')
    }else{
        reject('坐下来吃饭错误');
    }
}
function step3(resolve,reject){
    console.log('3.开始收拾桌子洗碗');
    if(state=1){
        resolve('收拾桌子洗碗完成')
    }else{
        reject('收拾桌子洗碗错误');
    }
}
new Promise(step1).
then(function(val){
    console.log(val);
    return new Promise(step2);
}),
then(function(val){
    console.log(val);
    return new Promise(step3);
}),
then(function(){
    console.log(val);    
});