encountered an undefined value

[zdwork]

var res string
chromedp.EvaluateAsDevTools("window.scrollTo(0,document.body.scrollHeight);",&res),

Hello, this printing error
2019/11/27 18:06:54 encountered an undefined value

[mvdan]

If you run that in your browser console, it does return undefined. Why are you trying to obtain the result as a string?

Please think about these issues before filing new issues. I do not offer free support for questions that can be solved with a bit of thinking and googling.

[zdwork]

res runtime.RemoteObject

You can't do this only once

[mvdan]

Sorry, but I don't understand.

[mvdan]

Closing because I still don't know what this is about.

[zhangguanzhang]

chromedp.EvaluateAsDevTools("window.scrollTo(0,document.body.scrollHeight);a="1",&res),

[welldonexing]

what the hell is chromedp.Evaluate function juse a undefined result ,why to case panic in go , that is holy shit code

[ahmetb]

@mvdan I think I understand what they are saying.

If chromedp.Evaluate action returns an undefined value, it currently results in this mentioned error. They are trying to figure out a way to ignore that. I think the easy way is to add || true to the command they're running.

Perhaps the way to solve this in the library could be to relax the requirement on the res parameter and require it only if there's a return value (that is, not "undefined"). This way, if the Evaluate returns "undefinded, and res==nil,

[ZekeLu]

A note for whom encounters the same issue and gets here: besides constructing the javascript to make sure it returns a value other than undefined (as suggested by @ahmetb), we can use runtime.RemoteObject to capture the undefined value:

Please note that res should be of type *runtime.RemoteObject instead of runtime.RemoteObject.

var res *runtime.RemoteObject
chromedp.EvaluateAsDevTools("window.scrollTo(0,document.body.scrollHeight);",&res),

[ZekeLu]

After #816 is merged, you can simply write:

EvaluateAsDevTools("window.scrollTo(0,document.body.scrollHeight);", nil),