CODEWITHSUNDEEP
javascriptnode.jsasync-awaitpuppeteer
user1584421
user1584421

Reputation: 3843

Puppeteer - using await inside loop

I am trying to check if there are specific number of elements with a specific class name. In case they are less than the number, keep scrolling down.

This is the code i used.

await page.evaluate(() => {
        while (await page.$$('.Ns6lhs9 _gfh3').length < counter) { 
            window.scrollBy(0, window.innerHeight);
        }
    });

This snippet of code is contained inside an async function.

Unfortuantely i get this error message:

C:\pup\test.js:27
        while (await page.$$('.Ns6lhs9 _gfh3').length < counter) {
                     ^^^^

SyntaxError: Unexpected identifier
    at createScript (vm.js:80:10)
    at Object.runInThisContext (vm.js:139:10)
    at Module._compile (module.js:616:28)
    at Object.Module._extensions..js (module.js:663:10)
    at Module.load (module.js:565:32)
    at tryModuleLoad (module.js:505:12)
    at Function.Module._load (module.js:497:3)
    at Function.Module.runMain (module.js:693:10)
    at startup (bootstrap_node.js:188:16)
    at bootstrap_node.js:609:3

Upvotes: 1

Views: 2225

Answers (2)

Benjamin Gruenbaum
Benjamin Gruenbaum

Reputation: 276266

The error

You need to mark the function you're passing inside as async, an async function is only lexically scoped to the function itself.

Any functions you call inside it (like .forEach or evaluate in this case) need to be marked as async themselves (assuming they support it):

//            Here
page.evaluate(async () => {

Fixing the larger issue

In your specific case, you should extract the loop outside of the evaluate to avoid timeouts:

while(await page.$$('.Ns6lhs9 _gfh3').length < counter) {
  await page.evaluate(() => window.scrollBy(0, window.innerHeight);
}

If your evaluate takes too long puppeteer will time out and it is generally preferable to not do expensive stuff inside evaluate.

Upvotes: 4

CJBLOC
CJBLOC

Reputation: 82

try this:

await page.evaluate( async () => {
    while (await page.$$('.Ns6lhs9 _gfh3').length < counter) { 
        window.scrollBy(0, window.innerHeight);
    }
});

The callback of evaluate needs async prefixed.

Upvotes: 0

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