How to get querySelectorAll from another webpage?

Question

I'm trying to get data from another webpage, using the HTML DOM. I tried code from another StackOverflow question (querySelectorAll() to html from another page) but it's not working for me:

let url = "[URL here]"
let xml = new XMLHttpRequest()
xml.onreadystatechange = function() {
  if (xml.readyState == 4) {
    let container = document.implementation.createHTMLDocument().documentElement
    container.innerHTML = xml.responseText
    let nodeList = container.querySelectorAll('.msDetails-Row')
    console.log(nodeList)
  }
}
xml.open("GET", url, false)
xml.send(null)

The nodeList is empty in the console log. However, when I run the code, querySelectorAll('.msDetails-Row'), on the actual URL, it works.