react/packages/shared/warning.js

/**
 * Copyright (c) 2013-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.
 */

/**
 * Similar to invariant but only logs a warning if the condition is not met.
 * This can be used to log issues in development environments in critical
 * paths. Removing the logging code for production environments will keep the
 * same logic and follow the same code paths.
 */

let warning = () => {};

if (__DEV__) {
  const printWarning = function(format, ...args) {
    let argIndex = 0;
    const message = 'Warning: ' + format.replace(/%s/g, () => args[argIndex++]);
    if (typeof console !== 'undefined') {
      console.error(message);
    }
    try {
      // --- Welcome to debugging React ---
      // This error was thrown as a convenience so that you can use this stack
      // to find the callsite that caused this warning to fire.
      throw new Error(message);
    } catch (x) {}
  };

  warning = function(condition, format, ...args) {
    if (format === undefined) {
      throw new Error(
        '`warning(condition, format, ...args)` requires a warning ' +
          'message argument',
      );
    }
    if (!condition) {
      printWarning(format, ...args);
    }
  };
}

export default warning;