inspect.js

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow strict
 */

import nodejsCustomInspectSymbol from './nodejsCustomInspectSymbol';

/**
 * Used to print values in error messages.
 */
export default function inspect(value: mixed): string {
  switch (typeof value) {
    case 'string':
      return JSON.stringify(value);
    case 'function':
      return value.name ? `[function ${value.name}]` : '[function]';
    case 'object':
      if (value) {
        const customInspectFn = value[String(nodejsCustomInspectSymbol)];
        if (typeof customInspectFn === 'function') {
          return customInspectFn();
        } else if (typeof value.inspect === 'function') {
          return value.inspect();
        } else if (Array.isArray(value)) {
          return '[' + value.map(inspect).join(', ') + ']';
        }

        const properties = Object.keys(value)
          .map(k => `${k}: ${inspect(value[k])}`)
          .join(', ');
        return properties ? '{ ' + properties + ' }' : '{}';
      }
      return String(value);
    default:
      return String(value);
  }
}