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Motion · 09 Stable Keys
Series contents · Technology map
Stage: Layout and Presence · Editable example · Storage ID: motion-step-09
Goals and learning outcomes
- Learning outcome: Explain the role of Identity. Input case: Different notes on each card.
- Deliverable: An ID-to-note mapping table before and after sorting. Connect your rationale for handling Local state to the code.
Prerequisites
Prepare the results of the Layout and Transform interpolation exercises from Unit 8, “Measuring Layout”.
Key concepts and explanations
Identity
A React key represents an item's identity. An array index can refer to a different item after reordering.
Local state
An input value must stay with its card. Data associations need separate validation even when the animation looks natural.
Practice setup
First check the execution scope guidance on the example screen. The following describes the environment needed to extend the assignment in a separate project. The existing motion-01·02·03 examples are limited examples based on Motion JS animate. For React layout, AnimatePresence, and hooks exercises, install motion in a separate local React project and import from motion/react. Do not assume JSX runs directly in the editor; preserve CSP and isolation.
The linked example is a starting point. It does not implement every task below. Complete work beyond its supported scope in a separate project.
Practice tasks
- In src/day-9.tsx of a separate exercise project, add input fields to ID key and index key lists, then sort them. Use the existing Unit 1·14·28 examples only as starting points.
- Input condition: Different notes on each card. Baseline: index. Run under the baseline condition, then record observations and errors in notes/day-9.md.
- Variable to change: key; new value: item.id. Run again with the same input path. Deliverable to save: An ID-to-note mapping table before and after sorting. Hypothesis to test: Notes stay with the correct cards. Compare it with the actual results and record whether they agree and the causes of any differences.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| key | index | item.id | Notes stay with the correct cards. |
Predictions in this table are not measured results. Change one condition at a time and record why the actual result differs.
Completion criteria
- Required deliverable: An ID-to-note mapping table before and after sorting. You have results for both the baseline and changed conditions, allowing a comparison of 2 conditions, and have recorded the input values and execution environment.
- Your explanation of the differences between the two conditions connects both concepts: Identity and Local state. For unexpected items, give at least 1 cause or reason they remain unresolved.
Self-check
- Which processing stage does Identity affect in this exercise? Input case: Different notes on each card.
- Variable to change: key. Hypothesis to test: Notes stay with the correct cards. Did the actual results agree with the hypothesis? Explain your evidence in terms of Local state.
Official references
Linked example and execution scope
Example source · Runtime environments and limits
Interactive Stable Keys experiment with cleanup of the resources used.
Source code and records are not overwritten automatically. Resetting an existing example also preserves your notes.