extract a javascript object value from a html page using goquery and otto

package main

import ( "errors" "log" "os"

"github.com/PuerkitoBio/goquery"
"github.com/robertkrimen/otto"

)

func getMP4URL(id string) string { doc, err := goquery.NewDocument("https://vine.co/v/" + id) check(err)

// we want the first <script> tag from the html
firstScript := doc.Find("script").First()

vm := otto.New()

// otherwise window.POST_DATA will raise an reference error `ReferenceError: 'window' is not defined`
_, err = vm.Run("var window = {};")
check(err)

// eval the javascript inside the <script> tag
_, err = vm.Run(firstScript.Text())
check(err)

// traverse down the object path: window > POST_DATA > <videoID> > videoDashURL
wVal, err := vm.Get("window")
check(err)

pdata, err := getValueFromObject(wVal, "POST_DATA")
check(err)

videoData, err := getValueFromObject(*pdata, id)
check(err)

videoDashUrl, err := getValueFromObject(*videoData, "videoDashUrl")
check(err)

// finally the video url...
videoUrl, err := videoDashUrl.ToString()
check(err)

return videoUrl

}

func main() { if len(os.Args) != 2 { log.Fatalln("Usage: vineUrl ") }

log.Println("Video URL:", getMP4URL(os.Args[1]))

}

// fatal if there is an error func check(err error) { if err != nil { log.Fatal(err) } }

func getValueFromObject(val otto.Value, key string) (*otto.Value, error) { if !val.IsObject() { return nil, errors.New("passed val is not an Object") }

valObj := val.Object()

obj, err := valObj.Get(key)
if err != nil {
	return nil, err
}

return &obj, nil

}