Fetch: Headers.

Describes the interface for a Fetch API compliant structure containing HTTP headers; this includes both the header names (as keys), and the header values, including multiple values per header, as applicable. Effectively, the fetch headers object acts as a container (as a JsMultiMap, specifically of all strings).

Mutability

Headers can be expressed in mutable or immutable form. For example, when headers are used as inputs for a request (meaning the values originate from another machine), they are expressed in immutable form. To mutate such headers, the developer can simply construct a mutable copy using one of the constructors available via FetchHeaders.Factory.

Rendering headers

Multiple header values, by spec, can often be reduced to comma-separated values within the same header name. Child implementations are expected to provide a render function which performs this task from held values.

Inheritors