Stage 2 Draft / December 3, 2024

Map.prototype.getOrInsert

Introduction

Given a key and a value, the getOrInsert method will return the existing value if it exists, or otherwise insert the provided default value and return that value.

Similarly, given a key and a callback function, the getOrInsertComputed method will return the existing value if it exists, or otherwise insert the returned value of the callback function, and return that value.

1 Map.prototype.getOrInsert ( key, value )

When the getOrInsert method is called the following steps are taken:

  1. Let M be the this value.
  2. Perform ? RequireInternalSlot(M, [[MapData]]).
  3. Set key to CanonicalizeKeyedCollectionKey(key).
  4. For each Record { [[Key]], [[Value]] } p of M.[[MapData]], do
    1. If p.[[Key]] is not empty and SameValue(p.[[Key]], key) is true, return p.[[Value]].
  5. Let p be the Record { [[Key]]: key, [[Value]]: value }.
  6. Append p to M.[[MapData]].
  7. Return value.

2 Map.prototype.getOrInsertComputed ( key, callbackfn )

When the getOrInsertComputed method is called the following steps are taken:

  1. Let M be the this value.
  2. Perform ? RequireInternalSlot(M, [[MapData]]).
  3. If IsCallable(callbackfn) is false, throw a TypeError exception.
  4. Set key to CanonicalizeKeyedCollectionKey(key).
  5. For each Record { [[Key]], [[Value]] } p of M.[[MapData]], do
    1. If p.[[Key]] is not empty and SameValue(p.[[Key]], key) is true, return p.[[Value]].
  6. Let value be ? Call(callbackfn, undefined, « key »).
  7. For each Record { [[Key]], [[Value]] } p of M.[[MapData]], do
    1. If p.[[Key]] is not empty and SameValue(p.[[Key]], key) is true, then
      1. Set p.[[Value]] to value.
      2. Return value.
  8. Let p be the Record { [[Key]]: key, [[Value]]: value }.
  9. Append p to M.[[MapData]].
  10. Return value.

3 WeakMap.prototype.getOrInsert ( key, value )

When the getOrInsert method is called the following steps are taken:

  1. Let M be the this value.
  2. Perform ? RequireInternalSlot(M, [[WeakMapData]]).
  3. If CanBeHeldWeakly(key) is false, throw a TypeError exception.
  4. For each Record { [[Key]], [[Value]] } p of M.[[WeakMapData]], do
    1. If p.[[Key]] is not empty and SameValue(p.[[Key]], key) is true, return p.[[Value]].
  5. Let p be the Record { [[Key]]: key, [[Value]]: value }.
  6. Append p to M.[[WeakMapData]].
  7. Return value.

4 WeakMap.prototype.getOrInsertComputed ( key, callbackfn )

When the getOrInsertComputed method is called the following steps are taken:

  1. Let M be the this value.
  2. Perform ? RequireInternalSlot(M, [[WeakMapData]]).
  3. If IsCallable(callbackfn) is false, throw a TypeError exception.
  4. If CanBeHeldWeakly(key) is false, throw a TypeError exception.
  5. For each Record { [[Key]], [[Value]] } p of M.[[WeakMapData]], do
    1. If p.[[Key]] is not empty and SameValue(p.[[Key]], key) is true, return p.[[Value]].
  6. Let value be ? Call(callbackfn, undefined, « key »).
  7. For each Record { [[Key]], [[Value]] } p of M.[[WeakMapData]], do
    1. If p.[[Key]] is not empty and SameValue(p.[[Key]], key) is true, then
      1. Set p.[[Value]] to value.
      2. Return value.
  8. Let p be the Record { [[Key]]: key, [[Value]]: value }.
  9. Append p to M.[[WeakMapData]].
  10. Return value.

A Copyright & Software License

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© 2024 Jonas Haukenes, Daniel Minor

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