spec.emu

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<pre class="metadata">
title: Upsert
stage: 2.7
contributors: Jonas Haukenes, Daniel Minor
markEffects: true
</pre>

<emu-intro id="intro">
  <h1>Introduction</h1>
  <p>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.</p>
  <p>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.</p>
</emu-intro>

<emu-clause id="sec-map.prototype.getOrInsert">
  <h1>Map.prototype.getOrInsert ( _key_, _value_ )</h1>
  <p>When the getOrInsert method is called the following steps are taken:</p>
  <emu-alg>
    1. Let _M_ be the *this* value.
    1. Perform ? RequireInternalSlot(_M_, [[MapData]]).
    1. Set _key_ to CanonicalizeKeyedCollectionKey(_key_).
    1. 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]].
    1. Let _p_ be the Record { [[Key]]: _key_, [[Value]]: _value_ }.
    1. Append _p_ to _M_.[[MapData]].
    1. Return _value_.
  </emu-alg>
</emu-clause>

<emu-clause id="sec-map.prototype.getOrInsertComputed">
  <h1>Map.prototype.getOrInsertComputed ( _key_, _callback_ )</h1>
  <p>When the getOrInsertComputed method is called the following steps are taken:</p>
  <emu-alg>
    1. Let _M_ be the *this* value.
    1. Perform ? RequireInternalSlot(_M_, [[MapData]]).
    1. If IsCallable(_callback_) is *false*, throw a *TypeError* exception.
    1. Set _key_ to CanonicalizeKeyedCollectionKey(_key_).
    1. 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]].
    1. Let _value_ be ? Call(_callback_, *undefined*, « _key_ »).
    1. NOTE: The Map may have been modified during execution of _callback_.
    1. 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_.
        1. Return _value_.
    1. Let _p_ be the Record { [[Key]]: _key_, [[Value]]: _value_ }.
    1. Append _p_ to _M_.[[MapData]].
    1. Return _value_.
  </emu-alg>
</emu-clause>

<emu-clause id="sec-weakmap.prototype.getOrInsert">
  <h1>WeakMap.prototype.getOrInsert ( _key_, _value_ )</h1>
  <p>When the getOrInsert method is called the following steps are taken:</p>
  <emu-alg>
    1. Let _M_ be the *this* value.
    1. Perform ? RequireInternalSlot(_M_, [[WeakMapData]]).
    1. If CanBeHeldWeakly(_key_) is *false*, throw a *TypeError* exception.
    1. 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]].
    1. Let _p_ be the Record { [[Key]]: _key_, [[Value]]: _value_ }.
    1. Append _p_ to _M_.[[WeakMapData]].
    1. Return _value_.
  </emu-alg>
</emu-clause>

<emu-clause id="sec-weakmap.prototype.getOrInsertComputed">
  <h1>WeakMap.prototype.getOrInsertComputed ( _key_, _callback_ )</h1>
  <p>When the getOrInsertComputed method is called the following steps are taken:</p>
  <emu-alg>
    1. Let _M_ be the *this* value.
    1. Perform ? RequireInternalSlot(_M_, [[WeakMapData]]).
    1. If CanBeHeldWeakly(_key_) is *false*, throw a *TypeError* exception.
    1. If IsCallable(_callback_) is *false*, throw a *TypeError* exception.
    1. 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]].
    1. Let _value_ be ? Call(_callback_, *undefined*, « _key_ »).
    1. NOTE: The WeakMap may have been modified during execution of _callback_.
    1. 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_.
        1. Return _value_.
    1. Let _p_ be the Record { [[Key]]: _key_, [[Value]]: _value_ }.
    1. Append _p_ to _M_.[[WeakMapData]].
    1. Return _value_.
  </emu-alg>
</emu-clause>