no-map-spread.md

Pattern: Spread in map callback

Issue: -

Description

Using spread operators in Array.prototype.map callbacks to add properties creates unnecessary object allocations. Use Object.assign instead for better performance when mutation is acceptable.

Examples

Example of incorrect code:

const enhanced = items.map(item => ({
  ...item,
  timestamp: Date.now()
}));

const combined = data.map(d => ({
  ...d,
  ...extraData
}));

Example of correct code:

const enhanced = items.map(item => 
  Object.assign(item, { timestamp: Date.now() })
);

// If you need to prevent mutations
const enhanced = items.map(item => 
  Object.assign({}, item, { timestamp: Date.now() })
);