validate before accessing

Always validate that values exist and have expected properties before accessing them, especially when removing non-null assertions or performing type casting. Avoid making assumptions about value presence or type safety without explicit checks.

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Always validate that values exist and have expected properties before accessing them, especially when removing non-null assertions or performing type casting. Avoid making assumptions about value presence or type safety without explicit checks.

Key practices:

  • When removing non-null assertion operators (!), add explicit null/undefined checks
  • Validate input types before casting, especially with schema validation libraries
  • Use specific filtering logic instead of generic Boolean filtering that may exclude valid falsy values
  • Consider whether to pass empty objects vs undefined parameters based on actual usage

Example from the discussions:

// Risky - assumes route exists after removing non-null assertion
const route = this.looseRoutesById[d.routeId]

// Better - validate before use
const route = this.looseRoutesById[d.routeId]
if (!route) return

// Risky - Boolean filter excludes valid falsy numbers like 0, -1
paths.filter(Boolean).join('/')

// Better - explicit check for meaningful values
paths.filter((val) => val !== undefined && val !== null).join('/')

This prevents runtime errors from null reference exceptions and ensures code behaves correctly with edge case values.

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