new Promise(function(resolve, reject){
    //异步调用成功
    resolve(传递给then的参数);
    //异步调用失败
    reject(传递给catch的参数);
}).then(function(resolve传递过来的参数){
    return new Promise(function(resolve, reject){
        //异步调用成功
        resolve(传递给then的参数);
        //异步调用失败
        reject(传递给catch的参数);
    });
}).then(function(resolve传递过来的参数){
    return new Promise(function(resolve, reject){
        //异步调用成功
        resolve(传递给then的参数);
        //异步调用失败
        reject(传递给catch的参数);
    });
});