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Class: ReadOnlyChainMap

Defined in: src/chain_map.ts:32

A chain map groups multiple records together to create a single, read-only view exposing a standard Record<string, unknown> interface.

Internally mappings are stored on a stack. Property resolution searches records on the stack from top to bottom, allowing properties from records at the top of the stack to mask properties from records at the bottom of the stack.

In the event that a property does not exist in the chain, property access resolves to [Nothing] - the symbol used to indicate the absence of a property rather than a property with a falsy or undefined value. This avoids the need to call x in chainMap before chainMap[x] in some cases.

New records can be pushed onto and popped off the stack using [ChainPush]() and [ChainPop](), respectively.

ReadOnlyChainMap is itself a Record<string, unknown>, so chain maps can be arbitrarily nested.

ReadOnlyChainMap does not copy or freeze supplied records. Changes made to records after they are added to the chain are immediately reflected in the composite view.

Indexable​

[key: string]: unknown

Constructors​

Constructor​

new ReadOnlyChainMap(...maps): ReadOnlyChainMap

Defined in: src/chain_map.ts:35

Parameters​

maps​

...Readonly<Record<string, unknown>>[]

Returns​

ReadOnlyChainMap

Methods​

[ChainKeys]()​

[ChainKeys](): string[]

Defined in: src/chain_map.ts:152

Compiles an array containing all unique keys across the stack hierarchy.

Returns​

string[]

[ChainPop]()​

[ChainPop](): Record<string, unknown> | undefined

Defined in: src/chain_map.ts:145

Pop and return the record off the top of the stack.

Returns​

Record<string, unknown> | undefined

[ChainPush]()​

[ChainPush](map): void

Defined in: src/chain_map.ts:138

Push map onto the top of the stack.

Parameters​

map​

Readonly<Record<string, unknown>>

Returns​

void

[ChainSize]()​

[ChainSize](): number

Defined in: src/chain_map.ts:170

Returns the total number of discrete map layers currently on the stack.

Returns​

number

[iterator]()​

[iterator](): Generator<[string, unknown], void, unknown>

Defined in: src/chain_map.ts:177

Iterates over the composite map view, yielding [key, value] pairs.

Returns​

Generator<[string, unknown], void, unknown>