await, then, return?

#help #javascript

Hi,

I'm using Sharp for compressing uploaded user images. I want to be sure that my approach is safe and performs in theory for all cases.

I'm rather hesitant, as I didn't set proper testing yet and for now I didn't deploy the app but doing big refactoring on the code then I will test everything the next days.

I am hesitant if my code is correct, and would like to hear from you also about it. Here it is:

const width_ = 200
try {
    thumbnailBuffer = await sharp(originalBuffer)
        .metadata()
        .then(({ width }) => {
            if(width > 400) {
                return sharp(originalBuffer)
                    .resize(Math.round(width * 0.5)).toBuffer()
            } else if(width > 200){
                return sharp(originalBuffer)
                    .resize(width_, { fit: 'inside' }).toBuffer()
            } else {
                return undefined
            }
        })
} catch (error) {
    req.log.error(`post/listings#postListingHandler#sharp: ${error.message}`)
}

Will thumbnailBuffer contain a value of a new buffer or a promise or this whole thing is incorrect ?

Thanks a lot !!

Top comments (5)

tq-bit • May 21 '22 • Edited

I've taken the code and modified it slightly. Like this, it seemed a bit easier to understand for me:

export async function resizeBuffer(originalBuffer) {
    const width_ = 200;
    try {
        const { width } = await sharp(originalBuffer).metadata();
        if (width > 400) {
            return sharp(originalBuffer)
                .resize(Math.round(width * 0.5))
                .toBuffer();
        }

        if (width > 200) {
            return sharp(originalBuffer).resize(width_, { fit: 'inside' }).toBuffer();
        }

        return undefined;
    } catch (error) {
        console.error(`post/listings#postListingHandler#sharp: ${error.message}`);
    }
}

The type of value this function returns is Promise<any>. More specifically:

If the image's width is greater than 400, it's resized to half its original size and a Buffer is returned inside a Promise
If the image's width is greater than 200 and lesser than 400, it's resized to 200 and a Buffer is returned inside a Promise
If the image's width is lesser than 200, undefined is returned inside a Promise

A hint of advice: If you're using VSCode, you can add the following line to you config file to enable simple type checks for Javascript:

"js/ts.implicitProjectConfig.checkJs": true,

aben • May 21 '22

Thanks a lot @tqbit I will take a look on the extension as well.
I found some examples in gists so I will write proper tests and experience with this.

Keff • May 21 '22

As far as I can tell, without knowing the sharp API at all, it seems that thumbnailBuffer will be a buffer is the width is greater that 200, otherwise it will be undefined.

aben • May 21 '22

Yes that what I intended to writing the code. But I meant JavaScript language speaking, does the return inside then return the value (here buffer/undefined) or a promise or go to heat...

Keff • May 21 '22

It should be the value, as you're using async/await.

DEV Community

await, then, return?

Top comments (5)

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