Afaik HTTP headers are always transferred as strings.

Could you elaborate on which headers accept booleans and numbers and why these cannot be provided as a string?

This update to require Record<string, string> broke backwards compatibility – booleans and numbers all toString() cleanly, so it makes this library a lot more user-friendly to accept other primitive types

i.e.

const headerA = 5; // simplified for example, imagine all of these headers came from something 
const headerB = false;
const headerC = 'someStr';
await axios.get(someUrl, { headers: { headerA, headerB, headerC } });

is a lot simpler from a user's perspective than

const headerA = 5; // simplified for example, imagine all of these headers came from something 
const headerB = false;
const headerC = 'someStr';
await axios.get(someUrl, { 
  headers: {
    headerA: headerA.toString(), 
    headerB: headerB.toString(), 
    headerC 
  } 
});

I thought about this as well, but I concluded that since HTTP headers are strings by definition and the types should reflect this. Also none of the official HTTP headers support the values true, false, or undefined, Internally axios doesn’t convert the header types in any way It just passes them directly into request.setRequestHeader(key: string, val: string).

There are some headers that support numeric strings, for example Access-Control-Max-Age. Although I don’t think axios should support numbers, I can see why this is convenient. If this is supported, I think it should be explicit (documented and tested).

@remcohaszing I can agree with that overall, makes sense. I guess my pain point is that this can be seen as a regression for any applications that were already using it in that way – If an app previously passed "Access-Control-Max-Age": 5 into Axios when the type was any, the 0.22.0 update now shows a TS error instead of converting it to a string for the user.

I thought about this and think it would make sense to also allow boolean and number values, but not undefined. My guess is that booleans will be converted to "0" or "1" and numbers accordingly, even if not by axios itself. But true, that would need to be tested.

@bfaulk96 Could you verify this using the network tab of your favorite browser's Dev Tools?

PS: You might want to rebase your branch on latest master, or merge latest master, as #4136 introduced two interface AxiosRequestHeaders and AxiosResponseHeaders, and your changes should only affect AxiosRequestHeaders.

I thought about this and think it would make sense to also allow boolean and number values, but not undefined. My guess is that booleans will be converted to "0" or "1" and numbers accordingly, even if not by axios itself. But true, that would need to be tested.

Values are simply cast to string. true becomes 'true', false becomes 'false', objects become '[Object object]', etc.

I think the axios maintainers should determine what values they want to support and the types should reflect this.

I thought about this and think it would make sense to also allow boolean and number values, but not undefined. My guess is that booleans will be converted to "0" or "1" and numbers accordingly, even if not by axios itself. But true, that would need to be tested.

Agreed. I got a little carried away with undefined, as that doesn't toString() nicely.

To answer the other question, yes:
5 -> "5"
true -> "true"

Those seem fairly harmless to allow – but I surely understand if not.

On the note of perhaps a a feature request – would be cool to allow Date but would require a transformer, as HTTP date headers are different format than date's toString. Would be nice though :D

Also, updated this branch to reflect our conversation – used the latest types already existing in master, and removed undefined as an allowed type.

Merged in latest changes 👍

Any update on this one? Do I need to do something/reach out to somebody? Or just be patient? 😄

@jasonsaayman what do you think?

Currently users have to explicitly pass strings as headers:

const maxAge = 1337;
const customHeader = true;

axios.get('/api', {
  headers: {
    'Access-Control-Max-Age': String(maxAge),
    'X-Custom-Header': String(customHeader)
  }
})

Basically these types say the following is also acceptable:

axios.get('/api', {
  headers: {
    'Access-Control-Max-Age': maxAge,
    'X-Custom-Header': customHeader
  }
})

@jasonsaayman any thoughts on this?

@bfaulk96 can you please have a look at the failing tests?

Done – sorry about that

@jasonsaayman Any chance of getting this merged?

bump

Yip will merge today

shouldn't this changes be added to response headers as well ?

shouldn't this changes be added to response headers as well ?

No, since HTTP Headers are always sent as strings, Response headers will be strings that you will need to parse if you want different types from them
For example, if I send "some-number": 5, the endpoint receiving my headers will receive "some-number": "5"

@jasonsaayman Any estimate on when the next Axios release might be?

@jasonsaayman Any estimate on when the next Axios release might be?

#4379 (comment)