How to pass parameters to async function in NodeJS?

Question

I'm Trying to take a screenshot from a website using the package puppeteer

For this I create a simple server with Express:

app.get('/requestScreenShootForDesktop/:id', function(req, res){
    (async () => {
        const pathUpload = 'uploads/' + Math.floor(Date.now() / 1000) + '.png';
        const browser = await puppeteer.launch();
        const page = await browser.newPage();
        await page.goto(this.req.params.id);
        await page.setViewport({width: 1920, height: 1080});
        await page.screenshot({path: pathUpload});

        await browser.close();
        await res.send({msg: 'ScreenShot Ok'});
      })();
});

The problem with this code is on line await page.goto(this.req.params.id);, Node says:

Cannot read property 'params' of undefined

This is because the variable req belonging to function app.get doesn't exists in async scope.

How can I solve this problem, and pass my variable to async function ?

The problem is not that req doesn't exist, it's that this.req doesn't exist. Why did you use this? Overall it's not really clear what you intend for that code to do. — Pointy
– Pointy, Commented Apr 28, 2019 at 14:30

Lawrence Cherone · Accepted Answer · 2019-04-28 14:49:14Z

2

Just ditch the IIFE and dont use this to access req

app.get('/requestScreenShootForDesktop/:id', async function(req, res){
    const pathUpload = 'uploads/' + Math.floor(Date.now() / 1000) + '.png';
    const browser = await puppeteer.launch();
    const page = await browser.newPage();

    await page.goto(req.params.id);
    await page.setViewport({width: 1920, height: 1080});
    await page.screenshot({path: pathUpload});

    await browser.close();

    res.send({msg: 'ScreenShot Ok'});
});

edited Apr 28, 2019 at 14:49

answered Apr 28, 2019 at 14:44

Lawrence Cherone

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6 Comments

Jonas Wilms Over a year ago

What should that change?

Lawrence Cherone Over a year ago

my bad I had missed the usage of this

Jonas Wilms Over a year ago

That is still a typo?

Lawrence Cherone Over a year ago

whats a typo? please explain or better yet, answer

Jonas Wilms Over a year ago

this.res vs res. Thats just a typo.

|

Wang Liang · Accepted Answer · 2019-04-28 14:32:14Z

0

(async (req, res) => {
    const pathUpload = 'uploads/' + Math.floor(Date.now() / 1000) + '.png';
    const browser = await puppeteer.launch();
    const page = await browser.newPage();
    await page.goto(req.params.id);
    await page.setViewport({width: 1920, height: 1080});
    await page.screenshot({path: pathUpload});

    await browser.close();
    await res.send({msg: 'ScreenShot Ok'});
  })(req, res);

answered Apr 28, 2019 at 14:32

Wang Liang

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1 Comment

Jonas Wilms Over a year ago

There is no sense in using req and res as parameters.

Vuk Stanković · Accepted Answer · 2019-04-28 15:54:57Z

0

You can keep IIFE, but remove this keyword

answered Apr 28, 2019 at 15:54

Vuk Stanković

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