Fix: Construct 3 Local Storage Not Saving on Mobile

Here is how to fix Construct 3 Local Storage not saving on mobile. Your game saves high scores via Local Storage. Desktop and Android: works. iPhone user reports scores reset every launch. Or the user launches from an Instagram link and progress does not persist. Mobile browsers have storage quirks that Construct 3’s Local Storage plugin inherits.

The Symptom

Local Storage Set Item appears to succeed but values do not persist across sessions on mobile. On iOS specifically, or in in-app browser views. Same project works on desktop and some Android browsers.

What Causes This

Private browsing mode. iOS Safari in private mode blocks persistent storage. Set Item appears to work (no error) but data is wiped when the tab closes. Users often do not know they’re in private mode.

In-app browser restrictions. Instagram, Twitter, Discord in-app browsers have various storage restrictions. Some isolate storage per tab, some block entirely.

Async events missed. The plugin is async. Calling Set Item then immediately reading values via Get Item before On Item Set fires returns old values.

Storage quota exceeded. IndexedDB (the backend) has ~50 MB quota on mobile. Large saves silently fail when over quota.

Cookies/site data cleared. Mobile browsers periodically clear site data, especially for sites visited infrequently. Long-term saves require prompting users to add to home screen or install as PWA.

The Fix

Step 1: Use On Item Set for sequencing.

Save Button on clicked:
  LocalStorage: Set "score" to score_value
  // Do NOT immediately read the value

LocalStorage on item "score" set:
  // Confirmed save, show success
  Text: Set text to "Saved!"

LocalStorage on error "score":
  // Fallback path
  Text: Set text to "Save failed (private mode?)"

On Item Set fires after IndexedDB commits. On Error fires if the browser refused. Handle both.

Step 2: Detect private mode. When Local Storage writes fail repeatedly, assume private mode and show a message:

LocalStorage on error (*):
  Add 1 to save_failure_count
  If save_failure_count >= 2:
    Dialog: Show "Saves may not work. If using private browsing, disable it and refresh."

Two failures is a strong signal something is blocked. Inform the user rather than silently losing data.

Step 3: In-memory fallback. Cache data in Construct global variables during play. Attempt save regularly. If save succeeds later, in-memory and persistent match. If it never succeeds, the session’s progress at least works until the tab closes.

Every 30 seconds:
  LocalStorage: Set "progress" to global.progress

// Plus save on major events (level complete, boss defeat)

Step 4: Recommend install / add to home screen. PWA or home screen shortcuts give more persistent storage on mobile. After first save, prompt:

Dialog: "Add this game to your home screen to save progress permanently."
// iOS: user must do via Safari share menu
// Android: beforeinstallprompt event, use Browser plugin

Platform Detection

Detect mobile via the Platform Info plugin. Adjust behavior per platform:

System: On start of layout:
  If PlatformInfo.OS = "iOS":
    // Warn about private mode, suggest home screen
  Else If PlatformInfo.IsWebView:
    // In-app browser, caution user

Understanding the issue

This bug class falls into a pattern that's worth understanding beyond the specific case. In Construct 3, the underlying behavior is shaped by how the engine layers its abstractions - the public API you call, the runtime systems that respond, and the platform-specific implementations underneath. A bug at any layer can produce symptoms that look like they originate at a different layer. Triaging effectively means recognizing which layer the symptom belongs to, even when the gameplay code is what's visible.

The specific bug described above is the kind that surfaces during integration rather than unit testing. It depends on a combination of factors: the asset configuration, the runtime state, the platform's specific behavior. In isolation, each piece looks correct; in combination, the bug emerges. This is why thorough integration testing - playing the actual game in realistic conditions - catches things that automated tests miss.

Why this happens

The triage path for this kind of bug is long. The symptom appears in gameplay, but the cause is in a different system. The reporter describes the gameplay effect; the engineer has to translate that into a hypothesis about the underlying cause. Misdirection is common.

At the engine level, the behavior comes from a deliberate design decision in Construct 3. The engine team chose a particular trade-off - usually performance versus convenience, or generality versus specificity - and that trade-off has consequences when you push against it. Understanding the trade-off is what turns 'this bug is mysterious' into 'this bug is the expected consequence of this design'.

Verifying the fix

Verifying this fix in isolation is straightforward: reproduce the bug, apply the change, confirm the bug no longer reproduces. The harder verification is regression - did this fix introduce a new bug elsewhere? Run your standard regression suite, plus any tests that exercise the same code path with different inputs.

Reproducibility is the prerequisite for verification. If you can't reliably reproduce the bug pre-fix, you can't reliably verify it post-fix. Spend time getting a clean reproduction before you write any fix code. The fix is fast once you understand the reproduction; the reproduction is the slow part.

Variations to watch for

Related bug classes often share the same root cause. If you find yourself fixing this issue, look for cousins: similar symptoms in adjacent systems, the same data flow but a different value, or the same fix pattern in another module. The catalog of 'we've seen this before' becomes valuable institutional knowledge.

Adjacent bugs often share a root cause. After fixing the case you've found, spend an hour searching the codebase for similar patterns. What's the same call with different arguments? The same data flow with a different entity type? The same lifecycle issue in a sibling system? Each match is a candidate for the same fix, or a related fix that prevents future bugs of the same class.

In production

Live games surface this bug class at scale. What's a rare edge case in development becomes a daily occurrence once you have a few thousand concurrent players. The class isn't 'this player has a unique setup'; it's 'one in N thousand sessions will trigger this exact combination'.

When triaging a similar issue in production, prioritize gathering data over hypothesizing causes. A player report describes a symptom; what you need is a build SHA, a session timestamp, and ideally a screen recording or session replay. With those, the bug becomes tractable. Without them, you're guessing at hypothetical reproductions that may not match what the player actually hit.

Performance considerations

If this issue manifests under high load (many actors, many particles, many network connections), profile the post-fix code path with realistic counts. The original cost was a bug; the new cost is real work, and real work has a budget.

Diagnostic approach

The diagnostic tools available depend on your engine and platform. Use the engine's native profilers and debug overlays before reaching for external tools. The native tools have context that external tools lack - they know which subsystem owns the code, which assets are loaded, and what state the engine is in.

For Construct 3-specific diagnostics, the editor's profiler is the canonical starting point. Capture a representative frame with the symptom present; compare against a frame without the symptom; the diff often points directly at the cause. If the symptom is non-deterministic, capture multiple frames and look for the pattern - the cause is usually a state transition or a specific input value rather than a continuous effect.

Tooling and ecosystem

Modern engine versions ship better tooling for this kind of issue than older versions. If you're on an older release, the diagnostic step may take significantly longer because the tools you'd want don't exist yet. Sometimes the right answer is upgrading rather than fighting through limited tooling.

Within Construct 3, the relevant diagnostic surfaces include the standard frame debugger, memory profiler, and engine-specific debug overlays. Each one shows a different facet of what's happening. The frame debugger reveals draw call ordering and state transitions; the memory profiler shows allocation patterns; the debug overlay reveals per-system state. Bugs that resist one tool usually surrender to another - the trick is knowing which tool to reach for first.

Edge cases and pitfalls

Boundary conditions deserve specific testing attention. What happens when the input is zero, maximum, negative, or NaN? What happens at the start of a session vs hours in? What happens at the boundary between two systems handling the same data? These are where bugs hide and where regression tests are most valuable.

When writing a regression test for this fix, focus on the boundary conditions that surfaced the original bug. Tests that exercise the happy path catch obvious regressions; tests that exercise the boundary catch the subtler regressions that look like new bugs but are really the original returning. The latter are the tests that earn their keep over the long life of the project.

Team communication

When this bug class affects multiple teams (often the case for cross-system issues), early communication prevents duplicate work. The team that owns the symptom may not own the cause. A 15-minute conversation at the start of triage often saves hours of independent investigation.

If this fix touches a system several engineers work in, a short writeup in the team's engineering channel helps. Not a full design doc - a paragraph explaining what was wrong, what's fixed, and what to watch for. Future engineers encountering similar symptoms will search for the fix; making it findable is a small investment that pays back later.

“Mobile storage is a best-effort system. Detect failures, fallback in memory, and educate users when platform limits bite.”

Related Issues

For Construct 3 collision issues, see Construct 3 Collision Not Detecting. For function patterns, Construct 3 Function Parameters Not Passed Correctly.

On Item Set for async. On Error for detection. In-memory fallback. Prompt install for persistence.