Javascript 循环、异步函数和 headless 浏览器

Question

通过使用微软新的 headless 浏览器 playwright，我构建了一些既不返回错误也不返回其他内容的东西。

此时，我的想法已经结束了，我请你给我一些提示，指出我的失败。

这段代码应该只是启动一个多头 headless 浏览器组异步。但是浏览器的启动挂起并且应用程序处于无限循环中。我将代码粘贴到此处，它是一个简单的 nodejs 脚本，用于重现该行为。

感谢帮助和阅读 ;)

const playwright = require('playwright');

log('start playwright async');

let maxRunners = 1;
let running = 0;
let list = [1,2,3,4,5,6,7,8,9,0,11,12,13,14,15];

log('start job');

while (list.length > 0) {

    if (running < maxRunners) {
        log('runner started');
        running++;

        let entry = list[0];
        list.shift();

        log('start browser loop');
        for (const browserType of ['chromium', 'firefox', 'webkit']) {
            log('fire async');
            (async () => {
                log('loop next');
                log('launch: ', browserType);
                const browser = await playwright[browserType].launch({
                    headless: false
                });
                log(browserType, ' launched');
                const context = await browser.newContext();
                log('open new page');
                const page = await context.newPage('http://whatsmyuseragent.org/');
                log('page opened');
                log('make screenshot');
                await page.screenshot({path: `example-${browserType}.png`});
                log('screenshot made');
                log('close browser');
                await browser.close();
                log('browser closed');
                log('loop succeed');

                running--;
            })();
            log('end async');
        }
        log('end loop');

        if (running === 0 && list.length === 0) {
            log('job finished');
        }
    }
}

log('end playwright script');

function log(...msgs) {
    let date = new Date();
    let timeString = date.toISOString().substr(11, 8);
    let msg = '';
    for (let i in msgs) {
        msg += msgs[i];
    }

    console.log(timeString, ':', msg);
}

输出:

20:53:29 : start playwright async
20:53:29 : start job
20:53:29 : runner started
20:53:29 : start browser loop
20:53:29 : fire async
20:53:29 : loop next
20:53:29 : launch: chromium
20:53:29 : end async
20:53:29 : fire async
20:53:29 : loop next
20:53:29 : launch: firefox
20:53:29 : end async
20:53:29 : fire async
20:53:29 : loop next
20:53:29 : launch: webkit
20:53:29 : end async
20:53:29 : end loop

Answer 1

您可以在代码中改进一些地方:

(async()=>{

  log('start playwright async');

  let maxRunners = 1;
  let running = 0;
  let list = [1,2,3,4,5,6,7,8,9,0,11,12,13,14,15];

  log('start job');
  const promises = [];
  while (list.length > 0) {

      if (running < maxRunners) {
          log('runner started');
          running++;

          let entry = list[0];
          list.shift();

          log('start browser loop');
          for (const browserType of ['chromium', 'firefox', 'webkit']) {
              log('fire async');
              promises.push((async () => {
                  log('loop next');
                  log('launch: ', browserType);
                  const browser = await playwright[browserType].launch({
                      headless: false
                  });
                  log(browserType, ' launched');
                  const context = await browser.newContext();
                  log('open new page');
                  const page = await context.newPage('http://whatsmyuseragent.org/');
                  log('page opened');
                  log('make screenshot');
                  await page.screenshot({path: `example-${browserType}.png`});
                  log('screenshot made');
                  log('close browser');
                  await browser.close();
                  log('browser closed');
                  log('loop succeed');

                  running--;
              })());
              log('end async');
          }
          log('end loop');
      } else {
        await Promise.all(promises);
      }
  }

  await Promise.all(promises);
  log('job finished');
  log('end playwright script');

  function log(...msgs) {
      let date = new Date();
      let timeString = date.toISOString().substr(11, 8);
      //date.setSeconds(45); // specify value for SECONDS here
      //var timeString = date.toISOString().substr(11, 8);
      let msg = '';
      for (let i in msgs) {
          msg += msgs[i];
      }

      console.log(timeString, ':', msg);
  }
})()

让我们将所有内容包装在一个异步函数中

(async()=>{
)();

然后，让我们跟踪这些任务/ promise :

const promises = [];
...
log('fire async');
promises.push((async () => {
})());

如果你离开了 worker ，你需要等待他们:

if (running < maxRunners) {
...
} else {
   await Promise.all(promises);
}

你应该开始使用它。