[sentry-junior]

onMutation can currently only accept or drop a whole mutation batch. The Replay SDK needs per-mutation control for two cases:

• [Replays] Ability to exclude specific DOM Elements from Mutation Tracking sentry-javascript#16831: mutations inside blocked elements still count toward mutationLimit, because onMutation runs before rrweb's block checks. Heavy SVG/D3 widgets can stop replays even when they are blocked.
• _experiments.ignoreMutations (feat(replay): Add _experiments.ignoreMutations option sentry-javascript#16816): it currently drops the whole batch if any one mutation matches, which also drops unrelated mutations.

This PR adds two things:

• onMutation may return a MutationRecord[]. rrweb then processes only that subset. Returning false still skips the batch. Returning true or nothing still processes everything.
• onMutation gets a second helpers argument with isBlocked(node). It uses the recorder's own blockClass/blockSelector/unblockSelector rules, checking ancestors too, so callers don't have to re-implement them.

Overhead is kept to a minimum. The helpers object is created once per observer, not per batch. isBlocked only runs when the caller invokes it, so the SDK can limit it to batches that exceed the mutation limit. The only new per-batch work is one Array.isArray check. This also drops the per-batch .bind() on processMutations, which is already an arrow-function property. Existing callers that return booleans behave the same.

via Francesco Gringl-Novy.

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View Junior Session [Sentry]

[logaretm]

There is a case where replay desyncs with the dom due to the dropped stuff but that was happening before already. So, LGTM!