SeleniumHQ/selenium · error · Error

CookieHeader must be an instance of Header. Received:'${head

Error message

CookieHeader must be an instance of Header. Received:'${header}'

What it means

Thrown by `ContinueResponseParameters.cookies()` when any element of the passed array is not a `Header` instance. Identical logic to the request-side cookies(): each element is serialized via `.asMap()`, so plain objects are rejected and the loop throws on the first bad element.

Source

Thrown at javascript/selenium-webdriver/bidi/continueResponseParameters.js:42

class ContinueResponseParameters {
  #map = new Map()

  constructor(request) {
    this.#map.set('request', request)
  }

  /**
   * Sets the cookies for the response.
   *
   * @param {Header[]} cookieHeaders - The array of cookie headers.
   * @returns {ContinueResponseParameters} - The current instance of the ContinueResponseParameters for chaining.
   * @throws {Error} - If the cookieHeader is not an instance of Header.
   */
  cookies(cookieHeaders) {
    const cookies = []
    cookieHeaders.forEach((header) => {
      if (!(header instanceof Header)) {
        throw new Error(`CookieHeader must be an instance of Header. Received:'${header}'`)
      }
      cookies.push(Object.fromEntries(header.asMap()))
    })

    this.#map.set('cookies', cookies)
    return this
  }

  /**
   * Sets the credentials for authentication.
   *
   * @param {string} username - The username for authentication.
   * @param {string} password - The password for authentication.
   * @returns {ContinueResponseParameters} The current instance of the ContinueResponseParameters for chaining.
   * @throws {Error} If username or password is not a string.
   */
  credentials(username, password) {
    if (typeof username !== 'string') {

View on GitHub (pinned to aa36b38e69)

Solutions

1. Build each entry as `new Header(name, new BytesValue(BytesValue.Type.STRING, value))`
2. Import `{ Header, BytesValue }` from `selenium-webdriver/bidi/networkTypes`
3. Ensure every element is a Header instance

Example fix

// before
params.cookies([{ name: 'Set-Cookie', value: 'sid=1; Path=/' }])
// after
const { Header, BytesValue } = require('selenium-webdriver/bidi/networkTypes')
params.cookies([new Header('Set-Cookie', new BytesValue(BytesValue.Type.STRING, 'sid=1; Path=/'))])

const { Header } = require('selenium-webdriver/bidi/networkTypes')
if (arr.every(h => h instanceof Header)) params.cookies(arr)

const { Header } = require('selenium-webdriver/bidi/networkTypes')
const allHeaders = (arr) => Array.isArray(arr) && arr.every(h => h instanceof Header)

When it happens

Trigger: Calling `params.cookies([{name:'Set-Cookie', value:'...'}])` with plain objects; passing `Cookie` instances instead of `Header` instances.

Common situations: Reusing the same plain-object array shape from request interception on the response side; building Set-Cookie headers as literals from config.

Related errors

• CookieHeader must be an instance of Header. Received:'${head
• Header value must be an instance of Header. Received:'${head
• Header value must be an instance of Header. Received:'${head
• Value must be an instance of BytesValue. Received: '${value}
• Value must be an instance of BytesValue. Received:'${value}'

AI-assisted analysis of SeleniumHQ/selenium@aa36b38e69 (2026-08-14). Data as JSON: /api/errors/625889a046333700. Report an issue: GitHub.