promise

    var axios = new Promise((resolve, reject) => {
        if(1==1){
            resolve("成功")
        }else{
            reject('失败')
        }
    })

    axios.then(res => {
        console.log(res);
    }).then(res => {
        console.log(res);
    })

promise相当于一个状态机

promise的三种状态

• pending
• fulfilled
• rejected

1.promise 对象初始化状态为 pending
2.当调用resolve(成功)，会由pending => fulfilled
3.当调用reject(失败)，会由pending => rejected