fix response headers types

[egmen]

some keys like 'set-cookie' are arrays https://github.com/axios/axios/blob/master/lib/helpers/parseHeaders.js#L45

[caugner]

It would probably make sense to introduce a specifc AxiosHeaders type:

type AxiosHeaders = Record<Exclude<"set-cookie", string>, string> & {
  "set-cookie"?: string[]
}

Note that it is also used in the AxiosTransformer and AxiosRequestConfiginterfaces:

axios/index.d.ts

Lines 1 to 3 in 6c00232

	export interface AxiosTransformer {
	(data: any, headers?: Record<string, string>): any;
	}

axios/index.d.ts

Lines 50 to 56 in 6c00232

	export interface AxiosRequestConfig<D = any> {
	url?: string;
	method?: Method;
	baseURL?: string;
	transformRequest?: AxiosTransformer | AxiosTransformer[];
	transformResponse?: AxiosTransformer | AxiosTransformer[];
	headers?: Record<string, string>;

[caugner]

You might want to wait until #4140 is merged, because it adds a new HeadersDefaults interface with essentially 11 occurences of Record<string, string> that could be replaced by the new AxiosHeaders type.

[bfaulk96]

@caugner #4144 does exactly that

[caugner]

@caugner #4144 does exactly that

👍 for differentiating RequestHeaders and ResponseHeaders, but this PR extends the type to string | string[], whereas #4144 extends the type to string | number | boolean | undefined.

The common ground would be to keep RequestHeaders as Record<string, string> and have ResponseHeaders distinguish between set-cookie (string[]) and other headers (string).

[bfaulk96]

@caugner #4144 does exactly that

👍 for differentiating RequestHeaders and ResponseHeaders, but this PR extends the type to string | string[], whereas #4144 extends the type to string | number | boolean | undefined.

The common ground would be to keep RequestHeaders as Record<string, string> and have ResponseHeaders distinguish between set-cookie (string[]) and other headers (string).

Haha sorry – I was referring to that PR assigning things to type aliases, I should have clarified that! Was sharing that the two PRs could build from one another 😄

[caugner]

Actually, #4117 was the first PR to suggest adding a Headers type.

[remcohaszing]

It would probably make sense to introduce a specifc AxiosHeaders type:

type AxiosHeaders = Record<Exclude<"set-cookie", string>, string> & {
  "set-cookie"?: string[]
}

I like this idea! But it doesn’t work. After some fiddling I came up with:

type AxiosHeaders = Record<string, string> & {
  "set-cookie"?: string[]
}

playground link

Also we may want to differentiate between request and response headers, as set-cookie is only defined as string[] in the response headers.

type AxiosRequestHeaders = Record<string, string>;

type AxiosResponseHeaders = Record<string, string> & {
  "set-cookie"?: string[]
};

[eyebrowkang]

It would probably make sense to introduce a specifc AxiosHeaders type:

type AxiosHeaders = Record<Exclude<"set-cookie", string>, string> & {
  "set-cookie"?: string[]
}

I like this idea! But it doesn’t work. After some fiddling I came up with:

type AxiosHeaders = Record<string, string> & {
  "set-cookie"?: string[]
}

playground link

Also we may want to differentiate between request and response headers, as set-cookie is only defined as string[] in the response headers.

type AxiosRequestHeaders = Record<string, string>;

type AxiosResponseHeaders = Record<string, string> & {
  "set-cookie"?: string[]
};

I have a question about this code, type AxiosResponseHeaders = Record<string, string> & { "set-cookie"?: string[] };, i wrote some codes here playground, but there are some error and i can't understand it, so could anyone help explain the reason?

[caugner]

i wrote some codes here playground, but there are some error and i can't understand it, so could anyone help explain the reason?

@EyebrowsWhite Not sure why it doesn't work when declaring the header object directly, but the following works (see playground):

type AxiosHeaders = Record<string, string> & {
  "set-cookie"?: string[]
}

declare let headers: AxiosHeaders;

headers = {}
headers['Content-Type'] = 'text/plain'
headers['set-cookie'] = ['abc', 'def']