SeleniumHQ/selenium · error · Error

Pattern must be an instance of UrlPattern. Received:'${patte

Error message

Pattern must be an instance of UrlPattern. Received:'${pattern}'

What it means

AddInterceptParameters.urlPatterns() iterates an array and validates each entry is an instance of UrlPattern. This is the batch variant of urlPattern(): any non-UrlPattern element in the array throws. The error message is slightly different from the single-pattern variant (no stray ')'), confirming these are two distinct throw sites.

Source

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

  urlPattern(pattern) {
    if (!(pattern instanceof UrlPattern)) {
      throw new Error(`Pattern must be an instance of UrlPattern. Received: '${pattern})'`)
    }
    this.#urlPatterns.push(Object.fromEntries(pattern.asMap()))
    return this
  }

  /**
   * Adds array of URL patterns to intercept.
   *
   * @param {UrlPattern[]} patterns - An array of UrlPattern instances representing the URL patterns to intercept.
   * @returns {AddInterceptParameters} - Returns the instance of AddInterceptParameters for chaining.
   * @throws {Error} - Throws an error if the pattern is not an instance of UrlPattern.
   */
  urlPatterns(patterns) {
    patterns.forEach((pattern) => {
      if (!(pattern instanceof UrlPattern)) {
        throw new Error(`Pattern must be an instance of UrlPattern. Received:'${pattern}'`)
      }
      this.#urlPatterns.push(Object.fromEntries(pattern.asMap()))
    })
    return this
  }

  /**
   * Adds string URL to intercept.
   *
   * @param {string} pattern - The URL pattern to be added.
   * @returns {AddInterceptParameters} - Returns the instance of AddInterceptParameters for chaining..
   * @throws {Error} - If the pattern is not an instance of String.
   */
  urlStringPattern(pattern) {
    if (typeof pattern !== 'string') {
      throw new Error(`Pattern must be an instance of String. Received:'${pattern}'`)
    }

View on GitHub (pinned to aa36b38e69)

Solutions

1. Ensure every array element is a UrlPattern instance built via new UrlPattern().
2. Separate structured patterns (urlPatterns) from string URLs (urlStringPatterns) into the correct method.
3. Dedupe node_modules so instanceof resolves against one UrlPattern class.
4. Filter out null/undefined entries before calling.

Example fix

// before
params.urlPatterns([
  { protocol: 'https', hostname: 'a.com' },
  { protocol: 'https', hostname: 'b.com' },
])

// after
const mk = (h) => new UrlPattern().protocol('https').hostname(h)
params.urlPatterns([mk('a.com'), mk('b.com')])

if (!Array.isArray(patterns)) throw new TypeError('urlPatterns expects an array')
patterns.forEach((p) => {
  if (!(p instanceof UrlPattern)) throw new TypeError('Each pattern must be a UrlPattern')
})

function areUrlPatterns(arr) {
  return Array.isArray(arr) && arr.every((p) => p instanceof UrlPattern)
}

When it happens

Trigger: Calling urlPatterns([{ protocol: 'https' }, ...]) with plain objects. Mixing UrlPattern instances and strings in the array (strings should go via urlStringPatterns). Passing an array containing null/undefined. Cross-realm UrlPattern instances where instanceof fails.

Common situations: Building the array from user/config data as plain objects. Mixing pattern types in one call instead of separating structured vs string patterns. Duplicate selenium-webdriver installs causing instanceof realm mismatch.

Related errors

• Pattern must be an instance of UrlPattern. Received: '${patt
• Pattern must be an instance of String. Received:'${pattern}'
• Params must be an instance of AddInterceptParameters. Receiv
• Params must be an instance of ContinueRequestParameters. Rec
• Params must be an instance of ContinueResponseParameters. Re

AI-assisted analysis of SeleniumHQ/selenium@aa36b38e69 (2026-08-14). Data as JSON: /api/errors/4b80cae65fdbe775. Report an issue: GitHub.