How to await inside setInterval in JS?

tinker picture tinker · Aug 13, 2018 · Viewed 16.7k times · Source

I have a code segment that looks like this:

async function autoScroll(page, maxDate = null) {
  await page.evaluate(async () => {
    await new Promise(async (resolve, reject) => {
        try {
            const scrollHeight = document.body.scrollHeight;
            let lastScrollTop = 0;

            const interval = setInterval(async () => {
                window.scrollBy(0, scrollHeight);
                const scrollTop = document.documentElement.scrollTop;
                let lastDate = null;

                if (maxDate) {
                    const html = new XMLSerializer().serializeToString(document.doctype) + document.documentElement.outerHTML;

                    await extractDate(html).then((date) => {
                        lastDate = date;
                    });
                }

                if (scrollTop === lastScrollTop || 
                    (maxDate && lastDate && maxDate.getTime() >= lastDate.getTime())) {
                    clearInterval(interval);
                    resolve();
                } else {
                    lastScrollTop = scrollTop;
                }
            }, 2000);
        } catch (err) {
            console.error(err);
            reject(err.toString());
        }
    });
});
}

Where extractDate method has the following form:

function extractDate(html) {
    return new Promise((resolve, reject) => {
        // Rest removed for brevity.
        resolve(result);
    });
}

Now the problem is that, my code keeps scrolling, but it doesn't wait for the other stuff inside setInterval to finish, as it keeps scrolling every 2 seconds, but normally extractDate function should take longer than 2 seconds, so I actually want to await for everything inside setInterval to finish before making the call to the new interval.

Because of the async nature of stuff, I didn't manage to console.log stuff so see the behavior of the code.

So, how can I make sure that everything inside setInterval finishes before making the next interval call?

EDIT:

This solution using setTimeout scrolls just once and throws unhandled promise rejection error with puppeteer.

 async function autoScroll(page, maxDate = null) {
     await page.evaluate(async () => {
        await new Promise(async (resolve, reject) => {
            try {
               const scrollHeight = document.body.scrollHeight;
               let lastScrollTop = 0;

                const interval = async function() {
                    window.scrollBy(0, scrollHeight);
                    const scrollTop = document.documentElement.scrollTop;
                    let lastDate = null;

                    if (maxDate) {
                        const html = new XMLSerializer().serializeToString(document.doctype) + document.documentElement.outerHTML;
                        await extractDate(html).then((date) => {
                            lastDate = date;
                        });
                    }

                    if (scrollTop === lastScrollTop || 
                       (maxDate && lastDate && maxDate.getTime() >= lastDate.getTime())) {
                        resolve();
                    } else {
                        lastScrollTop = scrollTop;
                        setTimeout(interval, 2000);
                    }
                }

                setTimeout(interval, 2000);

            } catch (err) {
                console.error(err);
                reject(err.toString());
            }
        });
    });
}

Answer

Zeeshan Ahmad picture Zeeshan Ahmad · Dec 26, 2018

Use the following code:

setInterval(async () => {
    await fetch("https://www.google.com/") 
}, 100);