处理承诺中的错误 [英] Processing errors in promises

问题描述

我试图弄清楚如何正确处理承诺链中的错误.几乎没有承诺，其中之一会引发错误.如果出现错误，我想终止链中的功能.

I try to figure out how to proper handle errors in promise chain. There are few promises and one of them throws error. In case of error I would like to terminate function in chain.

我面临的问题是:

1. 我们如何终止来自 catch 块的下一个调用?
2. 如何保证 then().catch().then() 链的执行顺序?在这我观察到在执行两个 then() 函数后调用了 catch 块.

代码示例:

function run() {
    test().then(function(data) {
        console.log("w3", "Print data: " + data);
    });
}

function test() {
    return new Promise(function(fulfill, reject) {
        ask()
            .catch(err => console.log("w3", "Process error from ask: " + err))
            .then(reply())
            .catch(err => console.log("w3", "Process error from reply: " + err))
            .then(function(data) {
                console.log("w3", "Finish test");
                fulfill(data);
                // TODO finish data
            })
    });
}

function ask() {
    return new Promise(function(fulfill, reject) {
        console.log("w3", "ask");   
        // fulfill("Hello");
        reject("Cancel Hello");
    });
}

function reply() {
    return new Promise(function(fulfill, reject) {
        console.log("w3", "reply");
        fulfill("World!");
        // reject("Cancel World");
    });
}

推荐答案

你只是在链条的末端.如果有什么错误.它将忽略其他 then 并直接捕获.

You just catch at the end of the chain. If there's any error. It will ignore the other then and go direct to catch.

function test() {
    return new Promise(function(fulfill, reject) {
        ask()
            .then(reply())
            .then(function(data) {
                console.log("w3", "Finish test");
                return fulfill(data); // <= Make sure to return here
                // TODO finish data
            })
            .catch(err => console.log("w3", "Process error from reply: " + err))
    });
}

确保返回 Promise 否则它不会捕获您的错误.

Make sure to return Promise or else it won't catch your error.

fulfill(data); 应该是 returnfulfill(data);

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