操纵up等待页面/DOM更新-响应在初始加载后添加的新项目 [英] puppeteer wait for page/DOM updates - respond to new items that are added after initial loading

问题描述

我想使用Puppeteer来响应页面更新.页面显示项目，当我离开页面时，随着时间的流逝，可能会出现新的项目.例如.每10秒就会添加一个新项目.

I want to use Puppeteer to respond to page updates. The page shows items and when I leave the page open new items can appear over time. E.g. every 10 seconds a new item is added.

我可以使用以下内容在页面的初始加载上等待一个项目:

I can use the following to wait for an item on the initial load of the page:

await page.waitFor(".item");
console.log("the initial items have been loaded")

我如何等待/接获将来的物品?我想实现这样的东西(伪代码):

How can I wait for / catch future items? I would like to achieve something like this (pseudo code):

await page.goto('http://mysite');
await page.waitFor(".item");
// check items (=these initial items)

// event when receiving new items:
// check item(s) (= the additional [or all] items)

推荐答案

您可以使用

You can use exposeFunction to expose a local function:

await page.exposeFunction('getItem', function(a) {
    console.log(a);
});

然后，您可以使用 page.evaluate 创建一个观察者并侦听创建的新节点在父节点中.

Then you can use page.evaluate to create an observer and listen to new nodes created inside a parent node.

此示例抓取(只是一个想法，而不是最后的工作) Stack Overflow中的python聊天，并打印在该聊天中创建的新项目.

This example scrapes (it's just an idea, not a final work) the python chat in Stack Overflow, and prints new items being created in that chat.

var baseurl =  'https://chat.stackoverflow.com/rooms/6/python';
const browser = await puppeteer.launch({headless: false});
const page = await browser.newPage();
await page.goto(baseurl);

await page.exposeFunction('getItem', function(a) {
    console.log(a);
});

await page.evaluate(() => {
    var observer = new MutationObserver((mutations) => { 
        for(var mutation of mutations) {
            if(mutation.addedNodes.length) {
                getItem(mutation.addedNodes[0].innerText);
            }
        }
    });
    observer.observe(document.getElementById("chat"), { attributes: false, childList: true, subtree: true });
});

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