Async await in a for loop

Question

Let's imagine I've got 2 awaits in a for loop, how can I make sure the first one is completed without throwing an error before executing the second await and thus looping again. I tried doing this using Puppeteer but it keeps looping even if the promise is not resolved...

for(var i = 0; i < 20; i++){
        console.log('loop started')
    await page1.goto('https://www.residentadvisor.net/dj.aspx?country=01').catch((err) =>{
        console.log('Page load fail : '+ err)
        if (err == 'Error: net::ERR_INTERNET_DISCONNECTED' || err == 'Error: net::ERR_NETWORK_CHANGED' || err == 'Error: net::ERR_NAME_NOT_RESOLVED'){
        let refreshIntervalId = setInterval(() =>{
           handleConnexionError(refreshIntervalId,page1)
        }, 5000) 
    }
    })
    console.log('Page loaded : ' + i)
    let teub = await page1.evaluate(() =>{
        return document.querySelector('a').innerText
    })
    console.log('Evaluate done : ' + teub )
    }



async function handleConnexionError(refreshIntervalId,page1){
    console.log('Retrying to connect')
    let errorHandle = true
    await page1.goto('https://www.residentadvisor.net/dj.aspx?country=01').catch(() => {
        errorHandle = false
    })
    if (errorHandle) {
        console.log('Succesfully Reconnected')
        clearInterval(refreshIntervalId)
        return true
    }
    else {
        console.log('Connection Fail Retrying in 10 sec ...')
    }
}

No, it does not keep looping when the promise is not resolved. The second part will wait until the first awaited promise is fulfilled. — Bergi
– Bergi, Commented Feb 7, 2018 at 0:08
What is handleConnexionError? Show it. Also, you probably want a try/catch around the await page1.goto() part instead of a .catch(). — acdcjunior
– acdcjunior, Commented Feb 7, 2018 at 11:06

Md. Abu Taher · Accepted Answer · 2018-02-08 18:24:29Z

You can create a new function and call it recursively on error.

/**
 * checks if error matches
 * @param {Object} err thrown error
 * @return {Boolean}
 */
async function shouldRetry(err) {
    return [
        "Error: net::ERR_INTERNET_DISCONNECTED",
        "Error: net::ERR_NETWORK_CHANGED",
        "Error: net::ERR_NAME_NOT_RESOLVED"
    ].includes(err);
}

/**
 * Function to Re navigate endlessly on error
 * @param {Object} config
 * @param {string} config.page the page instance
 * @param {String} config.url url to browse
 * @param {Number} config.delay delay for retry
 * @return {Promise}
 */
async function navigateUrl({ page, url, delay }) {
    try {
        // wait for page load
        const response = await page.goto(url);
        return response;
    } catch (error) {
        if (shouldRetry(error)) {
            // use a delay promise or the built in waitFor function
            await page.waitFor(delay);
            // re navigate
            return navigateUrl({ page, url, delay });
        } else {
            // throw on other errors
            throw new Error(error);
        }
    }
}

// now you can use them however you want
await navigateUrl({ page, 'http://example.com', 2000 });
await page.evaluate(() =>{
    return document.querySelector('a').innerText
});

It's best if you can keep things seperate, easier to write and maintain.

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