reproduce mergeHeaders typeerror

[belgattitude]

DO NOT MERGE, just a test, just downtracking

Related to #264.

• Reproduce type error failure on master branch -> 4cbc981 (breaks as expected)
• Testing a quick fix -> 7def7f3 (pass as expected)

[belgattitude]

@sholladay trying to fix the #264 in the constructor rather than in the mergeHeaders().

So here's the reproduction case when doing typecheck in the mergeHeaders (most browsers will assume undefined as {}, but this reproduce the case, looks a legit to me).

Fix is not not a problem.

Test for me is hard to do. Not used to ava, no constructor exposed. I appreciate your guidance

What I try to achieve:

• constructor
  • Given that inputis a string (ie: '/api/test')
    • the headers are taken from argument options.headers
  • Given than input is an URL or global.Request (and have headers defined).
    • the headers must be merged with arguments in options.headers

There's no reason why we would want to throw a type error when input is a string (it's part of the contract)

An exhaustive version of the constructor would reflect the idea +/- like this

class Ky {
  /**
   * @param {string|URL|globals.Request|null|undefined} input
   * @private
   */
  constructor(input, options = {}) {
   let headers;
   if (isObject(input) && isObject(input.headers)) {
     headers = mergeHeaders(input.headers,  isObject(options.headers) ? options.headers : {};);
   } else {
     headers = isObject(options.headers) ? options.headers : {};
   }
   /// here a lot more
   this._options = {
     headers
   }

awful ;)

The alternative approach still exists in my mind: setting default {} in mergeHeaders when the type is wrong.

I know modern browsers is what targets ky and this should not be needed.

But unluckiy this is a requirement here. A lot of errors in sentry for us

[belgattitude]

cause yes mergeHeaders will fail in edge 18 (maybe others too)...

[belgattitude]

This can be simplified ! just checking what's the practice here.

Possible

  this._options = {
    headers: mergeHeaders(this._input.headers || {}, options.headers);
  }

[belgattitude]

Closing as just it was included in #264