问题

以下是翻译的代码部分：

如下所示的代码中，我从一个函数中返回一个Promise。当Promise解决时，我想显示一个带参数的文本消息。换句话说，对于以下代码行：

resolve("成功保存数据到文件：",{fileName+newExt})

当Promise解决时，我收到上述文本，但没有`fileName+newExt`的值。

我尝试了以下方法：

resolve("成功保存数据到文件：",{d:fileName+newExt})
resolve("成功保存数据到文件：",fileName+newExt)

但始终只显示文本，而不显示`fileName+ext`的值。

**更新**

如下面发布的code2部分所示，我知道如何在Promise解决时打印消息。但是`resolve()`中的文本消息显示时没有`fileName+ext`的值。

**代码**

export function writeToFile(fileName, contents, ext='.tiff') {
    let newExt = ''
    return new Promise((resolve, reject) => {
        if (typeof (fileName) !== "string") {
            reject(new Error("fileName is not a string.你是否使用new String(..)传递了字符串对象？"))
        }

        if (contents == undefined) {
            reject(new Error("要写入文件的内容未定义"))
        }

        if (typeof (ext) !== "string") {
            reject(new Error("扩展名不是字符串。你是否使用new String(..)传递了字符串对象？"))
        }

        if (ext.charAt(0) === '.') {
            newExt = ext
        } else {
            newExt = '.' + ext
        }

        if (!fs.existsSync(envVars.DEBUG_OUTPUT_PATH_FOR_TIFFS)) {
            fs.mkdirSync(path, { recursive: true })
        }

        fs.writeFile(envVars.DEBUG_OUTPUT_PATH_FOR_TIFFS + fileName + ext, contents, { flag: 'w' }, (error) => {
            if (error) {
                reject(new Error("写入数据到文件时发生错误。错误信息：", error, " 文件：", fileName + newExt))
                throw error
            }
            resolve("成功保存数据到文件：",{d:fileName+newExt})
        });
    })
}

**代码2**

response.on('close', async () => {
    const bufferedData = Buffer.concat(data)
    writeToFile("test", bufferedData,'.tiff')
    .then(statusMsg => {
        console.log("write-to-file 状态消息：", statusMsg)
        fromFile(envVars.DEBUG_OUTPUT_PATH_FOR_TIFFS + "test" + envVars.CONST_TIFF_EXT)
        .then(geoTIFF => {
            geoTIFF.getImage()
            .then(geoTIFFImage => {
                console.log("geoTIFFImage:", geoTIFFImage.getBoundingBox())
            })
        })
    })
})

resolve("successfully saved the data to file:",{fileName+newExt})

resolve("successfully saved the data to file:",{d:fileName+newExt})
resolve("successfully saved the data to file:",fileName+newExt)

export function writeToFile(fileName,contents,ext='.tiff') {
let newExt = ''
return new Promise((resolve,reject)=> {
if (typeof (fileName) !== "string") {
reject(new Error("fileName is not a string.Did you pass string-object using new String(..)"))
}
if (contents == undefined) {
reject(new Error("contents to be written to the file is undefined"))
}
if (typeof (ext) !== "string") {
reject(new Error("extension is not a string.Did you pass string-object using new String(..)"))
}
if (ext.charAt(0) === '.') {
newExt = ext
} else {
newExt = '.' + ext
}
if (!fs.existsSync(envVars.DEBUG_OUTPUT_PATH_FOR_TIFFS)) {
fs.mkdirSync(path, {recursive:true})
}
fs.writeFile(envVars.DEBUG_OUTPUT_PATH_FOR_TIFFS + fileName + ext, contents,{flag:'w'},(error)=> {
if (error) {
reject(new Error("error occured while writing data to file.error:",error," file:",fileName+newExt))
throw error
}
resolve("successfully saved the data to file:",{d:fileName+newExt})
});
})

response.on('close', async()=>{
const bufferedData = Buffer.concat(data)
writeToFile("test", bufferedData,'.tiff')
.then(statusMsg => {
console.log("write-to-file status message:", statusMsg)
fromFile(envVars.DEBUG_OUTPUT_PATH_FOR_TIFFS + "test" + envVars.CONST_TIFF_EXT)
.then(geoTIFF=> {
geoTIFF.getImage()
.then(geoTIFFImage=> {
console.log("geoTIFFImage:",geoTIFFImage.getBoundingBox())
})
})
})

答案1

得分: 2

你不能从 Promise 中解析多个值，这就是你没有获取文件字符串或对象的原因。

因此，你应该更改从函数返回的结果。

例如，始终发送一个带有 message/result/error 属性的对象

resolve({message:'msg'});

错误情况也是一样的：

reject({message:error});

或者也可以使用数组或字符串，但只能是单个参数。

参考：

https://stackoverflow.com/questions/28703625/how-do-you-properly-return-multiple-values-from-a-promise

https://stackoverflow.com/questions/22773920/can-promises-have-multiple-arguments-to-onfulfilled

resolve({message:'msg'});

reject({message:error});

答案2

得分: 1

你应该使用 [JavaScript 模板字符串][1]

```typescript
resolve(`成功将数据保存到文件:${fileName}${newExt}`)

如果因某些原因你无法使用模板字符串，可以使用 + 符号进行连接:

resolve("成功将数据保存到文件:" + fileName + newExt)

然后可以这样调用你的函数:

writeToFile(fileName, contents, '.tiff').then(console.log).catch(console.error);

你也不需要同时使用 reject 和 throw。任何一个都会拒绝这个 promise，你可以像上面的示例那样使用 .catch((error) => console.error(error)) 来捕获错误。

<details>
<summary>英文:</summary>
You should use [JavaScript template literals][1]
```typescript
resolve(`successfully saved the data to file:${fileName}${newExt}`)

If for some reason you do not have access to template literals, use the + sign to concatenate:

resolve("successfully saved the data to file:" + fileName + newExt)

You can then call your function as follows:

writeToFile(fileName, contents, '.tiff').then(console.log).catch(console.error);

You also do not need to reject and to throw. Either one will reject the promise, and you can catch the error as shown on the example above with .catch((error) => console.error(error))