Finding/Returning Text - puppeteer

Question

I need to open very simple websites and scan for a json object i.e.
myJSONObject:["el1","el2"]. There is only one HTML <pre> tag on the site that contains 100s of lines of text. Nothing else.
I was planning on scanning the page for myJSONObject: and then return ["el1", "el2"].
I used the following, which returns true, as it finds "myJSONObject:", but I have no way to return any text.
const found = await page.evaluate(() => window.find("myJSONObject:"));
Is there a way to use a regexp or something to find the needed text and return it? Is this at all possible?
I am new to puppeteer, so I am unsure of its capabilities. I appreciate any feedback.

Answer 1

You already find the right function (puppeteer.evaluate) to do the job. With it you can return strings, objects, numbers or booleans (in fact any serializable/stringifyable value) from browser/page context to the node context.
Don't know if you already grasp this: browser/page context and node context are different. The only way you can transfer data between them is by stringifying the data and then transfer them.
Said that, to solve your problem you have to come up with a regex and return the string matched. Full working example:
Suppose the <pre> text is something like this: <pre>[...] myJSONObject:["el1","el2"] [...]</pre>
const puppeteer = require('puppeteer');
(async () => {
const browser = await puppeteer.launch();
const page = await browser.newPage();
await page.goto('https://example.com');
// setup test page
await page.evaluate(() => {
const pre = document.createElement('pre');
pre.innerText = '<pre>[...] myJSONObject:["el1","el2"] [...]</pre>';
document.body.append(pre);
});
// important part (this is the answer to your question)
const myJson = await page.evaluate(() => {
var re = /myJSONObject:(\[.*?])/; // regex to match "json text"
const pre = document.querySelector('pre').innerText;
const matchedJsonText = pre.match(re)[1];
const json = JSON.parse(matchedJsonText);
return json;
});
// show results
console.log('myJSONObject:', myJson);
await browser.close();
})();
Please note that this regex only work with the json you provided as example. You'll have to come up with a better regex to match the jsons that you need.