puppeteer/src/common/Debug.ts

/**
 * Copyright 2020 Google Inc. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

const isNodeEnv = typeof document === 'undefined';

/**
 * A debug function that can be used in any environment.
 *
 * If used in Node, it falls back to the
 * {@link https://www.npmjs.com/package/debug | debug module}. In the browser it
 * uses `console.log`.
 *
 * @param prefix - this will be prefixed to each log.
 * @returns a function that can be called to log to that debug channel.
 *
 * @example
 * ```
 * const log = debug('Page');
 *
 * log('new page created')
 * // logs "Page: new page created"
 * ```
 */
export const debug = (prefix: string): ((...args: unknown[]) => void) => {
  if (isNodeEnv) {
    // eslint-disable-next-line @typescript-eslint/no-var-requires
    return require('debug')(prefix);
  }

  // eslint-disable-next-line no-console
  return (...logArgs: unknown[]): void => console.log(`${prefix}:`, ...logArgs);
};