Add Headers to HeadersInit

[mhegazy]

Missed this in #315

[timocov]

It is not missed - I have did it specially because the spec does not have it :-)

[timocov]

For me this changes is a bit like change string[][] to [string, string][] - it is more correct and it will works but it does not correspond the spec.

[timocov]

@mhegazy so why this changes should be but [string, string][] not? :-)

[mhegazy]

record<ByteString, ByteString> is not really { [x:string]: string }. the later is much more restrictive than the earlier.

Header would be a valid record<ByteString, ByteString> but not a valid { [x:string]: string }. this was partially the behavior before the change by using object.

I did not want to go back to object, so just left it at Header which is a valid use case of this API, see https://developer.mozilla.org/en-US/docs/Web/API/Headers/Headers

[saschanaz]

the later is much more restrictive than the earlier.

Indeed, new Headers(new Map([['abc', 'bcd']])).get('abc') returns bcd on Firefox and Chrome.

[saschanaz]

new Headers({ [Symbol.iterator]() { return new Map([['abc', 'bcd']]).entries() } }).get('abc') returns bcd so I think we can check iterator type rather than adding Headers?

PS: Filed an issue for Edge returning null.

[saschanaz]

type Record<K, V> = { [Symbol.iterator](): IterableIterator<[K, V]> } | { [x: K]: V };

This should also work for URLSearchParams receiving records.

new URLSearchParams({ [Symbol.iterator]() { return new Map([['abc', 'bcd']]).entries() } }).toString()
// returns 'abc=bcd'

[mhegazy]

Headers is not iterable in --target ES5.. not sure what is the best way here. we can go back to object..

[saschanaz]

Filed microsoft/TypeScript#19806.

[timocov]

which is a valid use case of this API, see https://developer.mozilla.org/en-US/docs/Web/API/Headers/Headers

But it is not spec :)

Nobody known the truth: MDN has no case with string[][] as Headers ctor params, whatwg - Headers as Headers ctor params (and it is very strange) - I guess we need to use intersection of these specs and pass only { [key: string]: string } as valid Headers ctor params :)

[mhegazy]

I guess we need to use intersection of these specs and pass only { [key: string]: string } as valid Headers ctor params :)

that is not correct.. A Header is not { [key:string]: string }, and so is a Map<string, string>. which are all valid use cases of this API.

[timocov]

record<ByteString, ByteString> is not really { [x:string]: string }. the later is much more restrictive than the earlier.

@mhegazy could you please provide some examples to understand?

A Header is not { [key:string]: string }

Under as valid Headers ctor params I mean HeadersInit not Headers

[mhegazy]

Here is an example : https://github.com/firebase/firebase-js-sdk/blob/0a6ad04befd820ec52b05040e86ff52a62e37fa5/packages/messaging/src/models/token-manager.ts#L173-L198

Header should be a valid header value. but Header is not assignable to { [x:string]: string }.

[timocov]

@mhegazy Sorry, but I still cannot recognize the difference.

The spec says that Headers might be constructed from HeadersInit value.
HeadersInit in its turn should be sequence<sequence<ByteString>> or record<ByteString, ByteString>.
sequence<T> is lists of values of type T.
record<K, V> is ordered map with keys that are instances of K and values that are instances of V.

According to this I have a few questions:

1. Why you say that record<ByteString, ByteString> is not really { [x:string]: string }? Of course it should be { [key: ByteString]: ByteString } (or even Map<ByteString, ByteString> also) but seems that it is not important for now.

Header would be a valid record<ByteString, ByteString> but not a valid { [x:string]: string }.

What do you mean under Header: Headers or HeadersInit or something else (according the spec)?

3. What is valid header value?

Please correct me if I am somewhere wrong.

[mhegazy]

record<K,V> talks about own properties.. does not look at methods.. {[x:string]: string} applies to all members of the type, methods or properties.. that is why Header is not {[x:string]: string} in TS but is record<string, string> in the spec

[timocov]

Oh, I get it, thank you!