Changing document.title through JavaScript anonymous function

Question

I am still a bit new to JavaScript. I am trying to dynamically change the title of a page through javascript. However I am getting a result of undefined. I have tried multiple things and still no luck. What is the right way to pass a value to this anonymous function?

let email = "myemail@email.com"
await page.evaluate(  (email) => document.title = email );
console.log(await page.title());

why are you taking `email` as a param, shouldn't it be `() => document.title = email` — skara9, Dec 25 '21 at 00:10
@skara9 I just want to pass that variable into that function to set the page title — MaryCoding, Dec 25 '21 at 00:13
Does this answer your question? [How to dynamically change a web page's title?](https://stackoverflow.com/questions/413439/how-to-dynamically-change-a-web-pages-title) — Lars Flieger, Dec 25 '21 at 00:16
You can't arbitrarily pass in variables to a callback that way. Did you try the way skara showed you? — charlietfl, Dec 25 '21 at 00:25

score 2 · Accepted Answer · answered Dec 25 '21 at 00:17

2

I never used playwright js, but reading this documentation page here, https://playwright.dev/docs/evaluating, it looks like you pass arguments for the anonymous function as the second, and next parameters, of the evaluation method:

let email = "myemail@email.com"
await page.evaluate( (email) => document.title = email, email );
console.log(await page.title());

answered Dec 25 '21 at 00:17

TheFRedFox

600
3
12

This answered my issue perfectly! – MaryCoding Dec 25 '21 at 00:19
Also never used it, but presumably you can also use a closure, voiding the need for parameters in the first place: `await page.evaluate(() => document.title = email)` – Amadan Dec 25 '21 at 00:20
1

@Amadan nah it runs in a different execution context, so it doesn't have access to external variables – skara9 Dec 25 '21 at 00:21
@MaryCoding glad it helped. :) – TheFRedFox Dec 25 '21 at 00:22
Amadan and skara9 I am wondering that, too. Might be interesting to just try it. It's not impossible for a programming language to pass variables like that to inline functions. However, if it works here for playwright, I have no idea. ^^ – TheFRedFox Dec 25 '21 at 00:26

Changing document.title through JavaScript anonymous function

1 Answers1