zserge / lorca ui.Eval不返回任何值

Using github.com/zserge/lorca to pass HTML variables to a go func. When using lorca's Eval method to extract my variables, I'm not getting any returned vlaue.

My code

package main

import (
    "fmt"
    "net/url"

    "github.com/zserge/lorca"
)

var (
    ui1        lorca.UI
    HTML_entry string = `
<html>
    <body>
        <input hidden type="text" name="MYVAR" value="testVal">
        <input type="submit" onclick="golangfunc()"
    </body>
</html>
`
)

func main() {
    ui1, _ = lorca.New("data:text/html,"+url.PathEscape(HTML_entry), "", 480, 320)
    ui1.Bind("golangfunc", golangfunc)
    defer ui1.Close()
    <-ui1.Done()
}

func golangfunc() {
    htmlvar := ui1.Eval(`document.getElementsByName('MYVAR').value`).String()
    fmt.Println(htmlvar)
}