Do old cut-and-paste scripts still work in current browsers?

Why "it runs" is not the same as "it works"

Old scripts rarely throw a red error. More often the browser accepts the call and does nothing, or does something different from 2003. Deprecated features are a good example. MDN marks document.write() as deprecated and strongly discouraged, yet it still writes into the page when called from an inline <script> while the page is loading. Call it after the page has loaded and it clears the document first. Call it from an async or defer script and it is ignored, with a console message. Same function, three outcomes, depending on when it runs.

What happens to the common patterns now

Old pattern	What a current browser does	Source	What to use instead
window.status = "Welcome!"	Nothing: the HTML standard requires that setting it has no effect on the status bar	MDN, Window.status	Visible text on the page
document.write() after load or in an async script	Clears the page, or is ignored	MDN, Document.write	createElement and append, or textContent
window.open() on page load	Blocked: popups must open in direct response to user input, and window.open returns null when blocked	MDN, Window.open	A link, or a <dialog> inside the page
window.resizeTo() on the main window	Not allowed for a window or tab the page did not open with window.open(), or a window with several tabs	MDN, Window.resizeTo	Nothing; let the visitor size their window
<a href="javascript:...">	Runs on click, but misbehaves when copied, opened in a new tab, bookmarked, or when JavaScript fails	MDN, Window.open	A real href, with a click handler added on top
<script src="http://..."> on an HTTPS page	Blocked as mixed content	MDN, Mixed content	An HTTPS copy, or better, a local copy
oncontextmenu="return false" to stop right-click	Works for most clicks; Firefox shows the menu without firing the event on Shift plus right-click	MDN, contextmenu event	Nothing; it never protected the page
onclick="history.back()"	Does nothing if there is no previous page, for example in a new tab	MDN, History.back	A real link with a fallback address

The last row is the pattern behind the old site's most searched tip. The reviewed replacement is on the go back prompt page, which keeps a real link and uses history only for visitors who arrived from the same site.

Check a script in ten minutes

1. Save the snippet into a local file, for example test.html, with nothing else on the page.
2. Serve the folder instead of opening the file directly, so it behaves like a real page: python3 -m http.server 8000 --bind 127.0.0.1 from that folder (the --bind option binds it to localhost only, per the Python http.server docs, which also say the module is not for production), then open http://localhost:8000/test.html.
3. Open the browser's developer tools, switch to the Console tab and reload. Read every warning, not only the errors: blocked popups, ignored document.write() calls and mixed content all show up there.
4. Use the script with the keyboard alone. Tab to it, press Enter and Space. Most scripts from that era assumed a mouse.
5. Open the page in a new tab and from a bookmark. Anything that depends on history or document.referrer behaves differently there.
6. Turn on touch emulation in the developer tools and try again, since hover and mouse events do not map cleanly to touch.
7. Search the code for innerHTML, document.write, eval and http://. Each one is a reason to read that line twice.

If a script passes all seven, it works. If it fails one, decide whether the fix is a small edit or a rewrite.

Fix, replace or retire

The Script Shelf sorts the old CodeLifter scripts into three groups, and the same split works for anything you find in an old tutorial:

• Fix or rewrite when the job is still useful and the code is short: a quote rotator, a slideshow, a draggable box.
• Replace with the platform when the browser now does the job: input type="email" instead of an email checker, CSS scrollbar-color instead of a scrollbar script, a link rel="icon" instead of a favicon script.
• Retire when the job itself was the problem: popups nobody asked for, window resizing, right-click blocking.

The Script Shelf lists which old scripts went where and why. For the separate question of whether pasting code from an old site is safe, rather than whether it runs, see is it safe to paste a script from an old tutorial site. If the script you are looking at is a rollover, the rollover thread has a CSS replacement.