fix(upload): guard against envelope.data being null after async compress await

[Vitaliy Ponomarenko (ponomarenko)]

Problem

upload() is an async function. After the await compress(payload) call, the JS event loop is yielded. During that window a page navigation can trigger clarity.stop(), which calls envelope.stop() and sets envelope.data = null.

When the microtask resumes, the very next line:

send(payload, zipped, envelope.data.sequence, last);
//            ^^^^^^^^^^^^^^^^^^^ 💥 TypeError: Cannot read properties of null (reading 'sequence')

throws an unhandled promise rejection that Angular's Zone.js surfaces as an error.

The existing guard added by #894 (if (!envelope.data) return;) is placed before the await and therefore does not cover this post-await window.

This error is reproducible on Angular SPAs with frequent route transitions where Clarity flushes data at the moment the user navigates away.

Fix

1. Add a second null guard in upload() immediately after the await:

let zipped = last ? null : await compress(payload);
// Guard: stop() may have been called while compress() was awaiting (async race condition).
// envelope.stop() sets envelope.data = null, so we must re-check before accessing envelope.data.sequence.
if (!envelope.data) { return; }
metric.sum(Metric.TotalBytes, zipped ? zipped.length : payload.length);
send(payload, zipped, envelope.data.sequence, last);

2. Add a null guard in delay() which also reads envelope.data.sequence without any prior null check:

// Before:
let gap = ... : envelope.data.sequence * config.delay;

// After:
let gap = ... : (envelope.data ? envelope.data.sequence * config.delay : Setting.MinUploadDelay);

Root cause diagram

upload() starts           stop() fires during navigation
     │                           │
     ▼                           │
if (!envelope.data) return  ←  ✅ check passes, data is set
     │                           │
     ▼                           │
await compress(payload)  ─────── yields event loop ──────► envelope.stop() → data = null
     │                                                            │
     ▼                                                            │
metric.sum(...)                                                   │
send(..., envelope.data.sequence, ...)  ◄──── data is NULL here ─┘
                 💥 TypeError

[Copilot]

Pull request overview

Fixes an async race in clarity-js upload scheduling where envelope.data can become null during the await compress(payload) window (e.g., during SPA navigations that trigger clarity.stop()), preventing a TypeError from reading envelope.data.sequence.

Changes:

• Add a post-await null guard in upload() to avoid accessing envelope.data.sequence after shutdown.
• Add a defensive null guard in delay() to avoid reading envelope.data.sequence when envelope.data is null.

[Vitaliy Ponomarenko (ponomarenko)]

Any updates?