Materialize CSS + M.AutoInit: when to re-initialize versus destroy-and-recreate components after dynamic DOM updates

Short answer

There is no officially documented "sync" contract in Materialize 1.x that keeps JS instances aligned with declarative markup changes. The de facto safe pattern is destroy-then-reinit: before replacing or removing component markup, call getInstance(el).destroy(); after inserting new markup, initialize it explicitly. Some components happen to tolerate re-initialization without destroy, but that tolerance is undocumented and should not be relied on as a stable API.

What is confirmed versus inferred

Confirmed behavior (Materialize 1.x, vanilla JS):

• M.AutoInit() scans the DOM only at the moment it is called. Elements added later are never picked up automatically — there is no MutationObserver-style watching.
• Every component class exposes M.ComponentName.getInstance(element), which returns the live instance or null/undefined. This is the documented detection mechanism you asked about.
• Instances expose destroy(), which removes event listeners and cleans up references the component created.

Likely but not guaranteed: some components' init paths return an existing instance instead of double-initializing. Treat this as an implementation detail that can change between patch releases, not as a lifecycle contract.

The practical pattern

For an SPA-style render or AJAX fragment swap, scope initialization to the new subtree rather than re-running AutoInit globally:

function mountFragment(container, html) {
  // 1. Tear down instances in the old subtree before it is detached
  container.querySelectorAll('.modal, .sidenav, .dropdown-trigger, .tabs')
    .forEach(el => {
      ['Modal', 'Sidenav', 'Dropdown', 'Tabs'].forEach(name => {
        const inst = M[name].getInstance(el);
        if (inst) inst.destroy();
      });
    });

  // 2. Swap the markup
  container.innerHTML = html;

  // 3. Initialize only the new subtree
  container.querySelectorAll('.modal').forEach(el => M.Modal.init(el));
  container.querySelectorAll('.sidenav').forEach(el => M.Sidenav.init(el));
  // ...etc, or call M.AutoInit(container) if your build supports a root argument
}

Note the ordering: destroy before the DOM swap. Once you do innerHTML = '' or removeChild, the elements are detached and you can no longer reach their instances through the DOM — but the instances may still hold references and listeners, which is the leak/stale-reference risk you suspected. That risk is real even though the docs do not spell it out as a rule.

Can instances survive a DOM swap?

Only if the element node itself is preserved. If your renderer moves or re-inserts the same node (rather than serializing and re-parsing markup), the instance attached to it generally keeps working. If the node is destroyed and recreated from HTML strings, the old instance is orphaned and the new element has none — you must destroy the old (if still reachable) and init the new. Frameworks that diff the DOM (keeping stable nodes) are friendlier to Materialize than innerHTML replacement for this reason.

Verifying on your pinned version

Because behavior varies across 1.x patch releases, verify rather than trust:

1. Init a modal, then call M.Modal.getInstance(el) — confirm it returns an object, and after destroy() returns null again.
2. Remove a modal node without destroying, re-add identical markup, and try to open it. If you get duplicate backdrops or errors, your build does not self-heal — destroy-then-reinit is mandatory.
3. Check whether your version's M.AutoInit accepts a root element argument; if it does not, scope manual inits as shown above.

One detail that would change this advice: which rendering mechanism you use (string-based innerHTML versus a keyed/diffing renderer). With a diffing renderer that preserves nodes, you can often skip the destroy step entirely for untouched subtrees.