How to access LocalStorage?

Question

JavaScript

There is a site that, after loading, deletes the window.localStorage, copying it to a local variable. More or less like this:

(function () {
    let LS = window.localStorage;
    delete window.localStorage;
})();

I tried to solve the problem like this -

// ==UserScript==
// @name         Get LS
// @run-at       document-start
// @grant        window.localStorage
// ==/UserScript==

(function() {
    'use strict';
    const LS = window.localStorage;
    console.log(LS);
})();

But it works through time. Sometimes the site manages to remove localStorage, sometimes not.
Q: How can I be sure to copy local storage?

Answer 1

You need to make sure that the script is executed immediately when the window is created, somewhere before the scripts start loading, at the very top.
There is also such a trick as creating an empty iframe and extracting the desired property from its global window object.

var iframe = document.createElement("iframe");
iframe .style.display = "none";
document.documentElement.appendChild(iframe);
var localStorage = iframe.contentWindow.localStorage;