amark/gun · error · TypeError

Callback is not a function

Error message

Callback is not a function

What it means

yson.stringifyAsync serializes data asynchronously and delivers the result via a callback. It validates that the second argument is actually a function and throws a TypeError when it is not — catching cases where a non-callable (string, object, undefined) was passed in the callback position.

Source

Thrown at lib/ison.js:687

		throw new Error('Missing Callback');


  intensity = validateIntensity(intensity);
	return parseWrapper(data, reviver, intensity, callback);
};

  /**
  * Error checking  and call of appropriate functions for JSON stringify API
  * @param { primitive data types } data
  * @param { function or array } replacer
  * @param { number or string } space
  * @param { number } intensity
  * @param { function } callback
  * @return { function } stringifyWrapper
  */
yson.stringifyAsync = function(data, callback, replacer = null, space, intensity = 1) {
  if (typeof callback !== 'function') {
    throw new TypeError('Callback is not a function');
  }
  if (typeof space === 'number' || typeof space === 'string')
    space = validateSpace(space);
  if (typeof intensity === 'number')
    intensity = validateIntensity(intensity);
  return stringifyWrapper(data, replacer, space, intensity, callback);
}

if(typeof window != ''+u){ window.YSON = yson }
try{ if(typeof module != ''+u){ module.exports = yson } }catch(e){}
if(typeof JSON != ''+u){
	JSON.parseAsync = yson.parseAsync;
	JSON.stringifyAsync = yson.stringifyAsync;
}

}());

View on GitHub (pinned to 552227599d)

Solutions

1. Pass a function as the second argument: yson.stringifyAsync(data, (err, res) => { ... })
2. Verify argument order: callback is argument 2, replacer argument 3, space argument 4, intensity argument 5
3. Ensure the callback variable is defined and is a function at the call site
4. Wrap in a type check in dev: if (typeof cb !== 'function') throw before calling

Example fix

// before — old JSON.stringify order leaks replacer into callback slot
yson.stringifyAsync(data, replacer, 2, (err, res) => {});
// after
yson.stringifyAsync(data, (err, res) => {
  if (err) return console.error(err);
}, replacer, 2);

if (typeof callback !== 'function') {
  throw new TypeError('stringifyAsync requires a function callback');
}

const isFn = (v) => typeof v === 'function';
if (!isFn(cb)) throw new TypeError('callback must be a function');

try {
  yson.stringifyAsync(data, (err, res) => { if (err) throw err; }, replacer, space, intensity);
} catch (e) {
  console.error('stringifyAsync setup failed:', e.message);
}

When it happens

Trigger: Calling yson.stringifyAsync(data) with no callback; passing a non-function (e.g. a replacer string or space value) in the second position due to argument-order confusion with the signature (data, callback, replacer, space, intensity); a variable holding the callback being undefined at call time.

Common situations: Refactoring from synchronous JSON.stringify(value, replacer, space) and keeping the old argument order (replacer second) — here replacer must be third; copying stringify code that omitted the callback; typos in the callback variable name.

Related errors

• Missing Callback
• First argument must be a string, Buffer, ArrayBuffer, Array,
• Invalid first argument for type 'hex'.
• First argument must be Array containing ArrayBuffer or Uint8

AI-assisted analysis of amark/gun@552227599d (2026-09-02). Data as JSON: /api/errors/bcc8c0f2ed000090. Report an issue: GitHub.