javascript - 带有 promise.catch 和 console.log 的 NodeJS 错误？

Question

运行以下代码时，我会得到不同的结果，具体取决于我是否对 console.log("fnError: ", fnError) 进行了注释。这对我来说似乎很不对劲。

调用 console.log 会如何影响我的 promise ？

function run() {
    var fn = function(){
        throw new Error("incorrect message");
    };

    // returns a promise that should fail with
    // an error object whose .message is "correct message"
    var promisifiedFn = function(){
        return Promise.resolve()
            .then(fn)
            .catch((fnError) => {
                // commenting this out fixes things! //
                console.log("fnError: ", fnError);
                ///////////////////////////////////////

                fnError.message = "correct message";
                throw fnError;
            })
    }

    promisifiedFn().catch((e) => {
        console.log("caught error.message:", e.message);
        console.log("caught error:", e);
    });
}
run();

以上产生:

// fnError:  Error: incorrect message
//     at fn (/Users/sam/dev/ethereum/pennyeth/js/temp.js:18:9)
//     at <anonymous>
//     at process._tickCallback (internal/process/next_tick.js:169:7)
//     ...
// caught error.message: correct message
// caught error: Error: incorrect message
//     at fn (/Users/sam/dev/ethereum/pennyeth/js/temp.js:18:9)
//     at <anonymous>
//     at process._tickCallback (internal/process/next_tick.js:169:7)
//     ...

注意正在记录“不正确的消息”。如果你注释掉 console.log("fnError: ", fnError) 你会得到这个:

// caught error.message: correct message
// caught error: Error: correct message
//     at fn (/Users/sam/dev/ethereum/pennyeth/js/temp.js:18:9)
//     at <anonymous>
//     at process._tickCallback (internal/process/next_tick.js:169:7)
//     ....

运行 Node 8.0.0

Answer 1

这是预期的行为。

记录错误(至少通过 util.inspect 或 String)会评估其 .stack 属性。实例化错误对象时不会初始化堆栈字符串，而是延迟构建以节省内存。堆栈跟踪将包含错误消息，当您更改 .message 属性时，它会反射(reflect)或不反射(reflect)在堆栈跟踪中，具体取决于是否已经创建。

来自 the V8 stack trace API description :

For efficiency stack traces are not formatted when they are captured but on demand, the first time the stack property is accessed.

来自the official node Error documentation :

The string representing the stack trace is lazily generated when the error.stack property is accessed.