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 `ContinueRequestParameters.cookies()` when any element of the passed array is not a `Header` instance. The method iterates the array and calls `.asMap()` on each element, so plain `{name, value}` cookie objects are rejected even if their shape looks correct. The loop throws on the first bad element.

Source

Thrown at javascript/selenium-webdriver/bidi/continueRequestParameters.js:57

    if (!(value instanceof BytesValue)) {
      throw new Error(`Value must be an instance of BytesValue. Received: '${value})'`)
    }
    this.#map.set('body', Object.fromEntries(value.asMap()))
    return this
  }

  /**
   * Sets the cookies for the request.
   *
   * @param {Header[]} cookieHeaders - An array of cookie headers.
   * @returns {ContinueRequestParameters} - The current instance of the ContinueRequestParameters for chaining.
   * @throws {Error} - If a cookie header 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 headers for the request.
   *
   * @param {Header[]} headers - An array of Header objects.
   * @returns {ContinueRequestParameters} - The current instance of the ContinueRequestParameters for chaining.
   * @throws {Error} - If the header value is not an instance of Header.
   */
  headers(headers) {
    const headerList = []
    headers.forEach((header) => {

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 array element is a Header instance, not a plain object or a Cookie

Example fix

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

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:'session', value:'abc'}])` with plain objects; passing an array of mixed types; passing `Cookie` objects (the richer type from networkTypes) instead of `Header` objects.

Common situations: Confusing the cookies-as-headers representation required by continueRequest with the richer Cookie type; building the array from deserialized JSON; reusing plain cookie 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/cd848e4560acf88c. Report an issue: GitHub.