Facebook friends backup in web browser

facebook_friends_backup.js

/* Facebook friends backup in web browser
 * Scroll down to your friends page to load all profiles
 * Copy-paste the script below in a web browser console (F12 key or Ctrl+Shift+K shortcut in a browser like Firefox) and press enter
 * A textarea will appear at the end of the page so you can copy your friends list and paste it in a text file before saving it as a CSV file
 * You can then view your backup in a spreadsheet editor like LibreOffice Calc
 * You can also compare the backup with another one to see who removed you from their friends list (e.g. with the Linux diff command)
 * If the friend changed their name or profile URL, you can still find them with their profile ID which is backed up in the last column (open facebook.com/PROFILE_ID in a web browser)
 * The Facebook Graph API was not used because they are locking or deprecating most of their endpoints (e.g. https://developers.facebook.com/docs/graph-api/changelog/breaking-changes/#taggable-friends-4-4)
 */

var list = document.getElementsByClassName("uiProfileBlockContent");
var length = list.length;
var data = [];

for (var i = 0; i < length; ++i) {
	data[i] = list[i].firstElementChild.children[1].firstElementChild.firstElementChild.firstChild.nodeValue;
	data[i] += "\t" + list[i].firstElementChild.children[1].firstElementChild.firstElementChild.href;
	var json = JSON.parse(list[i].firstElementChild.children[1].firstElementChild.firstElementChild.getAttribute("data-gt"));
	if (json) { // JSON data is null when the Facebook profile is deactivated
		data[i] += "\t" + json.engagement.eng_tid; // get profile ID in case the Facebook user changes their profile URL
	}
}

var box = document.createElement("textarea");
box.value = data.join("\n");
document.body.appendChild(box);

What is a web browser console?

@hoshi411 it is a web browser area where you can execute custom JavaScript code, you can open it with the F12 key or Ctrl+Shift+K shortcut in a browser like Firefox (I just updated the script comment to mention this for people who are not familiar with it).