Given a `key`

and one or more mapping functions, the `upsert`

method will either remap an existing entry, insert a new entry from a mapping function, or both. `Upsert`

will return
the updated or inserted value.

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

- Let
`M`be thethis value. - Perform ? RequireInternalSlot(M, [[MapData]]).
- Let entries be the
List that is M.[[MapData]]. - If
IsCallable (updateFn) isfalse , andIsCallable (insertFn) isfalse , throw aTypeError exception. - Let
`entries`be theList that is`M`. - For each
Record { [[Key]], [[Value]] }`e`that is an element of`entries`, in original key insertion order, do- If e.[[Key]] is not empty and
SameValueZero (e.[[Key]],`key`) istrue then- If
IsCallable (updateFn) istrue then- Let
`updated`be ?Call (updateFn,undefined , « e.[[Value]],`key`,`M`») - Set
`e`.[[Value]] to`updated`. - Return
`e`.[[Value]]

- Let
- Return
`e`.[[Value]]

- If

- If e.[[Key]] is not empty and
- If
IsCallable (insertFn) istrue then

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

- Let
`M`be thethis value. - Perform ? RequireInternalSlot(M, [[WeakMapData]]).
- Let entries be the
List that is M.[[WeakMapData]]. - If
Type (`key`) is not Object, throw aTypeError exception. - If
IsCallable (updateFn) isfalse , andIsCallable (insertFn) isfalse , throw aTypeError exception. - Let
`entries`be theList that is`M`. - For each
Record { [[Key]], [[Value]] }`e`that is an element of`entries`, in original key insertion order, do- If e.[[Key]] is not empty and
SameValueZero (e.[[Key]],`key`) istrue then- If
IsCallable (updateFn) istrue then- Let
`updated`be ?Call (updateFn,undefined , « e.[[Value]],`key`,`M`») - Set
`e`.[[Value]] to`updated`. - Return
`e`.[[Value]]

- Let
- Return
`e`.[[Value]]

- If

- If e.[[Key]] is not empty and
- If
IsCallable (insertFn) istrue then

© 2019 Erica Pramer

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