': await 仅在异步函数中有效'

Question

在 node.js 中，我有一个 rest api，所有上传的图片都这么大，调整大小。

调整大小图像的文件路径被编译并返回。 下面是我的代码。 我得到错误

': await is only valid in async function'

我如何调用我的等待方法？ 我无法弄清楚代码。

app.post('/upload', upload.array('file'), async (req, res) => {
    var imagelist = [];
    for (const file of req.files) {         
        var sizeOf = require('image-size');
        sizeOf(__basefolder + file.originalname, function (err, dimensions) {
            //image quite big. resize it.
            if (dimensions.width > 128 && dimensions.height > 128) {
                console.log('more than 128');
               // ############### ERROR LINE BELOW ##################################
                const resize_2 = await resizeImage(__basefolder, file.originalname, dimensions, 2);
                imagelist.push([resize_2, file.originalname]);
            }
        });      
    };
    res.json(imagelist);
});

async function resizeImage(folder, fileName, dimensions, divisor) {
    return "resized image file path";
};

Answer 1

您需要使 CB function 异步，如：

sizeOf(__basefolder + file.originalname, async (err, dimensions) => {
            //image quite big. resize it.
            if (dimensions.width > 128 && dimensions.height > 128) {
                console.log('more than 128');
               // ############### ERROR LINE BELOW ##################################
                const resize_2 = await resizeImage(__basefolder, file.originalname, dimensions, 2);
                imagelist.push([resize_2, file.originalname]);
            }
        });   

Answer 2

您需要更改创建async function 的位置。

在 app.post 的回调app.post中不需要它，但是在sizeOf的回调中需要它，因为这是您await的包装 function

app.post('/upload', upload.array('file'), (req, res) => {
    var imagelist = [];
    for (const file of req.files) {         
        var sizeOf = require('image-size');
        sizeOf(__basefolder + file.originalname, async function (err, dimensions) {
            //image quite big. resize it.
            if (dimensions.width > 128 && dimensions.height > 128) {
                console.log('more than 128');
               // ############### ERROR LINE BELOW ##################################
                const resize_2 = await resizeImage(__basefolder, file.originalname, dimensions, 2);
                imagelist.push([resize_2, file.originalname]);
            }
        });      
    };
    res.json(imagelist);
});

async function resizeImage(folder, fileName, dimensions, divisor) {
    return "resized image file path";
};

这对您来说会变得很棘手，因为您将async包装在for...of循环中。

你最好在那个级别使用 await ；

async function* getImage(files) {
  for (file of files) {
    const {
      err,
      dimensions
    } = await sizeOf(__basefolder + file.originalname);
    if (dimensions.width > 128 && dimensions.height > 128) {
      console.log('more than 128');
      // ############### ERROR LINE BELOW ##################################
      const resize_2 = await resizeImage(__basefolder, file.originalname, dimensions, 2);
      yield [resize_2, file.originalname];
    }
  }
}

在您的 function 中，

for await (image of getImage()) {
  imagelist.push(image)
}

Answer 3

您需要使您的 function（在其中使用 await）成为异步 function。

这里有更多关于这个： https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function

喜欢：

app.post('/upload', upload.array('file'), async (req, res) => {
var imagelist = [];
for (const file of req.files) {         
    var sizeOf = require('image-size');
    sizeOf(__basefolder + file.originalname, async function (err, dimensions) {
        //image quite big. resize it.
        if (dimensions.width > 128 && dimensions.height > 128) {
            console.log('more than 128');
           // ############### ERROR LINE BELOW ##################################
            const resize_2 = await resizeImage(__basefolder, file.originalname, dimensions, 2);
            imagelist.push([resize_2, file.originalname]);
        }
    });      
};
res.json(imagelist);
});

async function resizeImage(folder, fileName, dimensions, divisor) {
  return "resized image file path";
};