Promise的链式调用

以setTimeout模拟网络请求的过程

        new Promise((resolve, reject) => {
                setTimeout(() => {
                    resolve("aaa");
                }, 1000);
            })
            .then((data) => {
                console.log(data);

                return new Promise((resolve, reject) => {
                    setTimeout(() => {
                        resolve(data + "bbb");
                    }, 1000);
                });
            })
            .then((data) => {
                console.log(data);

                return new Promise((resolve, reject) => {
                    setTimeout(() => {
                        resolve(data + "ccc");
                    }, 1000);
                });
            })
            .then((data) => {
                console.log(data);
            });

2.new Promise(resolve => resolve(结果))简写为Promise.resolve()

        new Promise((resolve, reject) => {
                setTimeout(() => {
                    resolve("aaa");
                }, 1000);
            })
            .then((data) => {
                console.log(data);

                return Promise.resolve(data + "bbb");
            })
            .then((data) => {
                console.log(data);

                return Promise.resolve(data + "ccc");
            })
            .then((data) => {
                console.log(data);
            });

3.省略Promise.resolve

        new Promise((resolve, reject) => {
                setTimeout(() => {
                    resolve("aaa");
                }, 1000);
            })
            .then((data) => {
                console.log(data);

                return data + "bbb";
            })
            .then((data) => {
                console.log(data);

                return data + "ccc";
            })
            .then((data) => {
                console.log(data);
            });