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To prevent a timed-out form request from creating a duplicate, give each logical submission an idempotency key, have the server bind that key to the request’s relevant content, and enforce key uniqueness in persistent storage. If the response is lost, retry the same operation with the same key. Dirty state helps decide whether the form needs saving; it does not tell you whether the server already processed a request.
Why a timeout can create a duplicate
A timeout tells the client that it did not receive a response in time. It does not establish whether the server received the request, completed its work, or committed the result before the connection failed. Because a repeated POST can cause additional effects, blindly sending it again may create a second record, charge, booking, or other operation. HTTP method semantics alone do not provide duplicate protection for every application; the endpoint needs a retry contract.
An idempotent submission flow lets the client safely ask about the same logical operation again. Stripe’s engineering guidance describes this failure ambiguity and the use of idempotency to ensure repeated calls produce a single set of side effects. The API must define what it supports and what response a retry receives.
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Dirty state answers whether the current form differs from a chosen baseline, usually the values loaded or last saved. In React Hook Form, isDirty represents whole-form dirtiness and dirtyFields tracks fields that differ from configured defaults. Reset behavior can change the baseline and which values or state are retained, so these flags depend on how the form is initialized and reset.
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- Use whole-form dirtiness to disable or suppress a redundant save when nothing changed.
- Use field-level dirtiness when the interface needs to identify which values changed.
- After a successful save, reset or update the baseline deliberately so the form reflects the saved state.
- During background refreshes, decide whether to retain edited values rather than unintentionally replacing them.
A pristine form can still need a retry if its prior request may have succeeded without a response. A dirty form can be submitted twice. Dirty-state handling improves the client experience, but only server-side operation identity and persistence can guard against duplicate effects.
Give each logical submission one idempotency key
When the user begins a new logical operation, generate an opaque key and associate it with that pending operation. Send it with the request using the header or request field the API documents. If the client times out and retries that same operation, resend the same key and the same request content. Generating a fresh key on every retry makes each attempt look like a new operation.
When the user makes a genuinely new submission, use a new key. Do not reuse an earlier key for changed form values: the server may treat that as an invalid replay rather than a new operation. MDN’s Idempotency-Key reference describes this convention, including example outcomes for missing keys, requests still being processed, and a key reused with different content. It also labels the header experimental and non-standard, so clients must not assume every server supports it.
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Track the key with the pending operation
The client should retain the key while that operation is unresolved, including across the retry path after a timeout. Clear or replace it only when the operation is resolved or the user intentionally starts a different one. The exact storage location and recovery behavior depend on the application; the important rule is that a retry represents the same operation, not merely another click.
Bind the key to a request fingerprint
A key identifies an operation, but by itself it does not prove that two requests carrying that key have the same content. A server can store a fingerprint of all or selected request fields alongside the key. If a later request reuses the key with a different fingerprint, the server can reject it instead of silently confusing a changed payload with the original operation.
Choose fingerprint inputs that define the business operation. Normalize those inputs consistently, and avoid making irrelevant transport details part of operation identity. The exact fields, canonicalization rules, hash algorithm, and handling of sensitive values are application-specific; there is no universal algorithm established by the cited MDN reference. Document the choice so that equivalent retries compare consistently.
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Make persistent storage arbitrate concurrent requests
An application-side “look up the key, then insert” check is not sufficient: two concurrent requests can both observe that the key is absent before either inserts. Put a unique constraint or unique index on the columns that define the key’s intended scope, then handle a uniqueness conflict by loading or returning the existing operation according to the endpoint’s replay policy.
For example, if keys are isolated per account, the uniqueness rule might cover (account_id, idempotency_key). If operations of different types have separate identities, the scope may also include an operation type. Choose columns to match the actual isolation boundary; a globally unique key and a scoped key are different designs.
PostgreSQL 18 documents that a unique constraint enforces uniqueness across its selected columns and creates a unique B-tree index. Its default handling treats NULL values as distinct, so a nullable key may allow multiple rows without a key. Require a key where appropriate or design null handling explicitly.
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Store enough state to coordinate retries
The persistent record needs to let the server distinguish an operation that is underway from one that has completed, and to apply the chosen replay behavior. Define the states, transaction boundaries, retention period, and recovery path for interrupted work as part of the API design. These details are not universal: an endpoint might return the original result for a completed retry, report that the first attempt is still processing, or apply another documented policy.
Choose a retry response and policy
Make the server’s behavior clear for each important case. A completed operation may return its prior outcome; an in-progress operation may tell the client to wait and retry; a same-key payload mismatch should surface as a conflict or other documented error. The status code and response body are part of the API contract, not a guarantee supplied by the header itself.
For transient failures, use bounded retries with exponential backoff and random jitter rather than having many clients retry immediately in sync. This reduces retry pressure during service trouble. Give the user useful status while waiting, and stop retrying when the failure is not transient or the API indicates that the request must be corrected.
- Timeout or lost response: retry the same operation with its original key and content.
- Operation still processing: wait according to the API’s guidance, then check or retry with the same key.
- Different payload under an existing key: correct the request or start a genuinely new operation with a new key, depending on the user’s intent.
- Fresh user intention: create a new key rather than reusing the previous operation’s identity.
Document the endpoint contract
Before shipping a retryable form, make these behaviors explicit for both client and server:
- Where the idempotency key is sent, its scope, and how long the server retains it.
- Which request fields define the fingerprint and how they are normalized.
- What the server returns for a completed replay, an operation in progress, a missing key, or a payload mismatch.
- How the client preserves a key across a retry and recognizes a new user intention.
- How persistent uniqueness conflicts map to the API’s replay behavior.
- How long and how often transient failures may be retried, including backoff and jitter.
These controls solve different parts of the problem: the form baseline helps avoid unnecessary saves, the key identifies one logical operation, the fingerprint catches key misuse, and the database constraint settles races. A reliable submission flow needs all the layers relevant to its behavior, not a dirty flag or a client-side double-click guard alone.
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