为什么这个承诺不会进入下一个“那么”？

Question

所以我有这个代码：

Parse.Cloud.define("apiCall", function(request, response) {

    return Parse.Cloud.httpRequest({
        // API call 1
    }).catch(function(error) {
        /// Only perform this if the first call fails

        // Return valid json here, to mock the Parse.Cloud.httpRequest below
        return Parse.Promise.as({"data": "this is an expected JSON"});

        return Parse.Cloud.httpRequest({
            // API call 2
        });
    }).then(
        function(httpResponse) {
            /// This should perform after call 1, or call 2 if call 1 failed

            return Parse.Cloud.httpRequest({
                // API call 3
            });
        }
    ).catch(
        function(error) {
            console.log('FAIL');
            return response.error(error);
        }
    );
});

我预计即使Call 1失败也会执行调用3，但显然它没有执行，它执行第一个catch块，但随后执行最后一个catch块。当我在catch区块中返回新的承诺时，我以为我正确地发现了错误？

Answer 1

简而言之，每个Promise链应该只有一个捕获块。

您可以使用async / await块重构代码，如下所示：

Parse.Cloud.define("apiCall", async function(request, response) {

    let response = null;
    try {
        response = await Parse.Cloud.httpRequest({
            // API call 1
        })
    } catch (error) {
        console.log({"data": "this is an expected JSON"});

        response = Parse.Cloud.httpRequest({
            // API call 2
        });
    }
    try {
        // Use response variable here
        let response2 = Parse.Cloud.httpRequest({
            // API call 3
        });
        return response2;
    } catch (error) {
        console.log('FAIL');
        return response.error(error);
    }
});

如果你想坚持使用Promise链，你也可以这样做：

Parse.Cloud.define("apiCall", function(request, response) {

    return new Promise((resolve, reject) => {
        Parse.Cloud.httpRequest({
            // API call 1
        })
        .then(function (data) {
            resolve(data);
        })
        .catch(function(error) {
            /// Only perform this if the first call fails

            // Return valid json here, to mock the Parse.Cloud.httpRequest below
            console.log({"data": "this is an expected JSON"});

            Parse.Cloud.httpRequest({
                // API call 2
            })
            .then(function (data) {
                resolve(data);
            })
            .catch(function (error) {
                reject(error);
            })
        })
    }).then(
        function(httpResponse) {
            /// This should perform after call 1, or call 2 if call 1 failed

            return Parse.Cloud.httpRequest({
                // API call 3
            });
        }
    ).catch(
        function(error) {
            console.log('FAIL');
            return response.error(error);
        }
    );
});