encountered an undefined value

[FournyP]

What versions are you running?

$ go list -m github.com/chromedp/chromedp
github.com/chromedp/chromedp v0.7.4
$ google-chrome --version
Chromium : 91.0.4472.164
$ go version
go version go1.16.6 windows/amd64

What did you do? Include clear steps.

Hi everyone, I have a function to set some id on select tags.

Here my code :

chromedp.ActionFunc(func(c context.Context) error { // Function to add ids on selects

        var err error
	var selects []*cdp.Node

	chromedp.Nodes("select", &selects, chromedp.ByQueryAll).Do(c)

	var buffer *runtime.RemoteObject

	for index, node := range selects {

		expression := "document.querySelectorAll('select')[" + strconv.Itoa(index) + "].setAttribute('id', '#')"

		if node.ChildNodeCount == 12 { // Month select
			expression = strings.ReplaceAll(expression, "#", "monthSelect")
			err = chromedp.Evaluate(expression, buffer).Do(c)
		} else if node.ChildNodeCount <= 31 && node.ChildNodeCount >= 28 { // Day select
			expression = strings.ReplaceAll(expression, "#", "daySelect")
			err = chromedp.Evaluate(expression, buffer).Do(c)
		} else { // Year select
			expression = strings.ReplaceAll(expression, "#", "yearSelect")
			err = chromedp.Evaluate(expression, buffer).Do(c)
		}

		if err != nil {
			return err
		}
	}

	return err
}),

I use the *runtime.RemoteObject as a buffer to handle the undefined result

However, I meet the error : encountered an undefined value

Maybe I do something wrong

What did you expect to see?

No error, but I want to handle the error if another occur

What did you see instead?

The error : encountered an undefined value

Have a good day, and thanks for your help

[ZekeLu]

If the result value of chromedp.Evaluate is of type runtime.RemoteObject, the parameter should be of type **runtime.RemoteObject. Here is the change to correct your code:

-err = chromedp.Evaluate(expression, buffer).Do(c)
+err = chromedp.Evaluate(expression, &buffer).Do(c)

What's more, if you don't care about the result value, you can just pass nil to the parameter res (since 0.7.3. see #816).

-err = chromedp.Evaluate(expression, buffer).Do(c)
+err = chromedp.Evaluate(expression, nil).Do(c)

I think the most simple way is to implement the logic with javascript and evaluate the javascript expression with a simple call to chromedp.Evaluate.

expression := `
document.querySelectorAll('select').forEach(s => {
    const childCount = s.children.length;
    const id = childCount === 12 ? 'monthSelect' :
        childCount >= 28 && childCount <= 31 ? 'daySelect' : 'yearSelect'
    s.setAttribute('id', id);
})
`
// ...
	chromedp.Evaluate(expression, nil),

[FournyP]

Hello @ZekeLu

It work

Thanks for your reply,

Have a good day