GoogleChrome/lighthouse · error · TypeError

Expected object but got ${typeof base}

Error message

Expected object but got ${typeof base}

What it means

Error "Expected object but got ${typeof base}" thrown in GoogleChrome/lighthouse.

Source

Thrown at core/config/config-helpers.js:98

 * @param {boolean=} overwriteArrays
 */
function _mergeConfigFragment(base, extension, overwriteArrays = false) {
  // If the default value doesn't exist or is explicitly null, defer to the extending value
  if (typeof base === 'undefined' || base === null) {
    return extension;
  } else if (typeof extension === 'undefined') {
    return base;
  } else if (Array.isArray(extension)) {
    if (overwriteArrays) return extension;
    if (!Array.isArray(base)) throw new TypeError(`Expected array but got ${typeof base}`);
    const merged = base.slice();
    extension.forEach(item => {
      if (!merged.some(candidate => isEqual(candidate, item))) merged.push(item);
    });

    return merged;
  } else if (typeof extension === 'object') {
    if (typeof base !== 'object') throw new TypeError(`Expected object but got ${typeof base}`);
    if (Array.isArray(base)) throw new TypeError('Expected object but got Array');
    Object.keys(extension).forEach(key => {
      const localOverwriteArrays = overwriteArrays ||
        (key === 'settings' && typeof base[key] === 'object');
      base[key] = _mergeConfigFragment(base[key], extension[key], localOverwriteArrays);
    });
    return base;
  }

  return extension;
}

/**
 * Until support of jsdoc templates with constraints, type in config.d.ts.
 * See https://github.com/Microsoft/TypeScript/issues/24283
 * @type {LH.Config.Merge}
 */
const mergeConfigFragment = _mergeConfigFragment;

View on GitHub (pinned to 9515cd4e58)

Solutions

1. Pass a plain object for this config property instead of the current value.
2. Use object syntax, e.g. {"key": "value"}, not an array or primitive.

When it happens

Trigger: Thrown during config extension when a base config value that must be merged as an object is not an object.

Common situations: See trigger scenarios.

AI-assisted analysis of GoogleChrome/lighthouse@9515cd4e58 (2026-08-13). Data as JSON: /api/errors/1566c51f04dc6379. Report an issue: GitHub.