testStringCoercion() — react Function Reference

Source Code

packages/shared/CheckStringCoercion.js lines 47–72

function testStringCoercion(value: mixed) {
  // If you ended up here by following an exception call stack, here's what's
  // happened: you supplied an object or symbol value to React (as a prop, key,
  // DOM attribute, CSS property, string ref, etc.) and when React tried to
  // coerce it to a string using `'' + value`, an exception was thrown.
  //
  // The most common types that will cause this exception are `Symbol` instances
  // and Temporal objects like `Temporal.Instant`. But any object that has a
  // `valueOf` or `[Symbol.toPrimitive]` method that throws will also cause this
  // exception. (Library authors do this to prevent users from using built-in
  // numeric operators like `+` or comparison operators like `>=` because custom
  // methods are needed to perform accurate arithmetic or comparison.)
  //
  // To fix the problem, coerce this object or symbol value to a string before
  // passing it to React. The most reliable way is usually `String(value)`.
  //
  // To find which value is throwing, check the browser or debugger console.
  // Before this exception was thrown, there should be `console.error` output
  // that shows the type (Symbol, Temporal.PlainDate, etc.) that caused the
  // problem and how that type was used: key, atrribute, input value prop, etc.
  // In most cases, this console output also shows the component and its
  // ancestor components where the exception happened.
  //
  // eslint-disable-next-line react-internal/safe-string-coercion
  return '' + (value: any);
}