dcaaef1011
Format: YYYY-MM-DD-description.md - 2026-01-19-infrastructure-deployment.md - 2026-01-19-backend-api-implementation.md (in progress) Co-Authored-By: Claude Sonnet 4.5 (1M context) <noreply@anthropic.com>
50 lines
1.7 KiB
Markdown
50 lines
1.7 KiB
Markdown
---
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title: Early Length Check for Array Comparisons
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impact: MEDIUM-HIGH
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impactDescription: avoids expensive operations when lengths differ
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tags: javascript, arrays, performance, optimization, comparison
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---
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## Early Length Check for Array Comparisons
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When comparing arrays with expensive operations (sorting, deep equality, serialization), check lengths first. If lengths differ, the arrays cannot be equal.
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In real-world applications, this optimization is especially valuable when the comparison runs in hot paths (event handlers, render loops).
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**Incorrect (always runs expensive comparison):**
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```typescript
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function hasChanges(current: string[], original: string[]) {
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// Always sorts and joins, even when lengths differ
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return current.sort().join() !== original.sort().join()
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}
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```
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Two O(n log n) sorts run even when `current.length` is 5 and `original.length` is 100. There is also overhead of joining the arrays and comparing the strings.
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**Correct (O(1) length check first):**
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```typescript
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function hasChanges(current: string[], original: string[]) {
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// Early return if lengths differ
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if (current.length !== original.length) {
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return true
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}
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// Only sort when lengths match
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const currentSorted = current.toSorted()
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const originalSorted = original.toSorted()
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for (let i = 0; i < currentSorted.length; i++) {
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if (currentSorted[i] !== originalSorted[i]) {
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return true
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}
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}
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return false
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}
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```
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This new approach is more efficient because:
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- It avoids the overhead of sorting and joining the arrays when lengths differ
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- It avoids consuming memory for the joined strings (especially important for large arrays)
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- It avoids mutating the original arrays
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- It returns early when a difference is found
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