SeleniumHQ/selenium · error · Error

Value must be an instance of BytesValue. Received: ${typeof

Error message

Value must be an instance of BytesValue. Received: ${typeof value} with value: ${value}

What it means

Thrown by ProvideResponseParameters.body() when the value argument is not an instance of BytesValue. The setter serializes the body via Object.fromEntries(value.asMap()), so it requires the BytesValue class. A raw string, buffer, or plain object is rejected because the BiDi response body must be a typed BytesValue.

Source

Thrown at javascript/selenium-webdriver/bidi/provideResponseParameters.js:41

 * @class
 */
class ProvideResponseParameters {
  #map = new Map()

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

  /**
   * Sets the body value for the response parameters.
   *
   * @param {BytesValue} value - The value to set as the body. Must be an instance of BytesValue.
   * @returns {ProvideResponseParameters} - Returns the ProvideResponseParameters object for chaining.
   * @throws {Error} - Throws an error if the value is not an instance of BytesValue.
   */
  body(value) {
    if (!(value instanceof BytesValue)) {
      throw new Error(`Value must be an instance of BytesValue. Received: ${typeof value} with value: ${value}`)
    }
    this.#map.set('body', Object.fromEntries(value.asMap()))
    return this
  }

  /**
   * Sets the cookie headers for the response.
   *
   * @param {Header[]} cookieHeaders - An array of cookie headers.
   * @returns {ProvideResponseParameters} - Returns the ProvideResponseParameters object for chaining.
   * @throws {Error} - Throws an 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}'`)
      }

View on GitHub (pinned to aa36b38e69)

Solutions

1. Wrap the body in a BytesValue: params.body(new BytesValue(BytesValue.Type.STRING, 'response body text')).
2. For binary bodies, encode as base64 and use new BytesValue(BytesValue.Type.BASE64, base64String).
3. If body is optional, simply omit the body() call instead of passing an empty/invalid value.

Example fix

// before
const params = new ProvideResponseParameters(id).body('Hello World')

// after
const { BytesValue } = require('selenium-webdriver/bidi/networkTypes')
const params = new ProvideResponseParameters(id)
  .body(new BytesValue(BytesValue.Type.STRING, 'Hello World'))

function toBody(v) {
  if (v instanceof BytesValue) return v
  if (typeof v === 'string') return new BytesValue(BytesValue.Type.STRING, v)
  throw new TypeError('body must be BytesValue or string')
}

function isBytesValue(v) {
  return v instanceof BytesValue
}

When it happens

Trigger: Calling params.body('response body text') (raw string), params.body(Buffer.from(...)), or params.body({type:'string', value:'v'}).

Common situations: Assuming body() accepts a plain string like fetch/Express APIs; passing a Node Buffer instead of a base64 BytesValue; deserializing a stored response object.

Related errors

• Params must be an instance of ProvideResponseParameters. Rec
• Value must be an instance of BytesValue. Received: '${value}
• CookieHeader must be an instance of Header. Received:'${head
• Header must be an instance of Header. Received:'${header}'
• Params must be an instance of AddInterceptParameters. Receiv

AI-assisted analysis of SeleniumHQ/selenium@aa36b38e69 (2026-08-14). Data as JSON: /api/errors/eb2ebbe963ee3191. Report an issue: GitHub.