fetch: improve util.inspect output for web specifications (#2938)

lib/web/fetch/headers.js

@@ -12,6 +12,7 @@ const {
 } = require('./util')
 const { webidl } = require('./webidl')
 const assert = require('node:assert')
+const util = require('util')
 
 const kHeadersMap = Symbol('headers map')
 const kHeadersSortedMap = Symbol('headers map sorted')
@@ -576,8 +577,18 @@ class Headers {
 
     return this[kHeadersList]
   }
+
+  [util.inspect.custom] (depth, options) {
+    const inspected = util.inspect(this[kHeadersList].entries)
+
+    return `Headers ${inspected}`
+  }
 }
 
+Object.defineProperty(Headers.prototype, util.inspect.custom, {
+  enumerable: false
+})
+
 iteratorMixin('Headers', Headers, kHeadersSortedMap, 0, 1)
 
 Object.defineProperties(Headers.prototype, {

test/fetch/headers-inspect-custom.js

@@ -0,0 +1,17 @@
+'use strict'
+
+const { Headers } = require('../../lib/web/fetch/headers')
+const { test } = require('node:test')
+const assert = require('node:assert')
+const util = require('util')
+
+test('Headers class custom inspection', () => {
+  const headers = new Headers()
+  headers.set('Content-Type', 'application/json')
+  headers.set('Authorization', 'Bearer token')
+
+  const inspectedOutput = util.inspect(headers, { depth: 1 })
+
+  const expectedOutput = "Headers { 'Content-Type': 'application/json', Authorization: 'Bearer token' }"
+  assert.strictEqual(inspectedOutput, expectedOutput)
+})