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Map vs WeakMap

  1. const map = new Map()
  2.  
  3. map.set(1, 'one')
  4.  
  5. console.log(map.get(1))
  6.  
  7. const weakMap = new WeakMap()
  8.  
  9. // this will fail with an error:
  10. // weakMap.set(1, 'one')
  11.  
  12. // console.log(weakMap.get(1))

Noticed this gotcha the other day. For some reason WeakMap can’t have integers as keys. After years of using WeakMap I guess I’ve only ever used objects as keys and assumed it could just have keys of any type. Using a Map instead solves the problem, but you’ll need to be careful to manager your references to properly clear the Map. Anyway, just one of those things… Maybe I’ll write more about it when I have some time to dig deeper.

// gotchas // javascript // objects // tricks

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