necolas/react-native-web · warning

message

Error message

message

What it means

warnOnce is a dev-only helper that prints a console.warn for a given key exactly once per session, then records the key in warnedKeys to suppress repeats. The literal message string 'message' appears when a caller passes a placeholder or wrong argument — i.e. the actual warning text was not supplied (or a variable holding it was empty/undefined-coerced) so the user sees the unhelpful string 'message'. It never runs in production (NODE_ENV === 'production' returns early).

Source

Thrown at packages/react-native-web/src/modules/warnOnce/index.js:25

 * @flow strict
 */

const warnedKeys: { [string]: boolean, ... } = {};

/**
 * A simple function that prints a warning message once per session.
 *
 * @param {string} key - The key used to ensure the message is printed once.
 *                       This should be unique to the callsite.
 * @param {string} message - The message to print
 */
export function warnOnce(key: string, message: string) {
  if (process.env.NODE_ENV !== 'production') {
    if (warnedKeys[key]) {
      return;
    }

    console.warn(message);

    warnedKeys[key] = true;
  }
}

View on GitHub (pinned to a9de220ba9)

Solutions

1. Find the warnOnce call site emitting the placeholder (extractNonStandardStyleProps or preprocess in style preprocessing) and pass the real deprecation text
2. Fix argument order: warnOnce(key, message) — ensure the descriptive string is the second argument
3. If you control the call, replace with the intended message e.g. warnOnce('displayInline', 'display: inline is not a valid...')
4. Check for upstream fix: this is an internal message bug — update react-native-web to a version where the call site text is correct

Example fix

// before
warnOnce('unsupportedStyle', 'message');
// after
warnOnce('unsupportedStyle', 'Unsupported style prop "' + name + '" will be ignored.');

function callWarnOnce(key, message) {
  if (typeof key !== 'string' || key.length === 0) throw new TypeError('warnOnce: key must be a non-empty string');
  if (typeof message !== 'string' || message.length === 0 || message === 'message') throw new TypeError('warnOnce: message must be a descriptive string');
  warnOnce(key, message);
}

function hasRealMessage(args) {
  return args.length >= 2 && typeof args[1] === 'string' && args[1].length > 0;
}

When it happens

Trigger: Calling warnOnce(key, 'message') with the literal placeholder, or warnOnce(key, someVar) where someVar is undefined/misordered so the second positional string defaults to a template placeholder; in react-native-web internals, extractNonStandardStyleProps and preprocess invoke warnOnce with style-prop deprecation messages — a regression or bad merge passing the wrong literal surfaces this.

Common situations: Upgrading react-native-web and hitting a deprecation warning whose text was mistakenly left as a placeholder; local forks/patches editing the message argument; custom style preprocessing code calling warnOnce with swapped arguments (key and message reversed or message omitted).

Related errors

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AI-assisted analysis of necolas/react-native-web@a9de220ba9 (2026-09-01). Data as JSON: /api/errors/6629b2612a581ce0. Report an issue: GitHub.