OrchardCMS/OrchardCore · error · Error

Syntax error, unrecognized expression:

Error message

Syntax error, unrecognized expression: 

What it means

jQuery's selector engine Sizzle throws this via Sizzle.error() when a selector string cannot be tokenized/parsed by Sizzle.tokenize. It means jQuery received a selector expression (as first arg to $(...) or inside :not(...), find(), etc.) that is syntactically invalid for the selector grammar supported by this jQuery version. The empty message (": ") means the offending expression was an empty string or the error was raised with an empty/whitespace value.

Solutions

1. Log/guard the selector before passing to $(): if (!sel || typeof sel !== 'string') return; or console.log the exact string that reaches Sizzle.error.
2. Fix the malformed selector string; validate it against standard CSS selector syntax supported by jQuery 3.6.
3. If the input may legitimately be empty, check for empty string and skip the lookup instead of calling $().
4. If a plugin throws it, update the plugin to a version compatible with jQuery 3.x.
5. As a last resort wrap dynamic selector use in try/catch and fall back to a document.querySelectorAll or default behavior.

Example fix

// before
var target = $($el.data('target'));

// after
var sel = $el.data('target');
var $target = (typeof sel === 'string' && sel.trim()) ? $(sel) : $();

function isValidSelector(sel) {
  return typeof sel === 'string' && sel.trim().length > 0;
}
// usage: if (isValidSelector(sel)) $(sel); else return $();

function isNonEmptyString(v) { return typeof v === 'string' && v.trim().length > 0; }

var $el;
try { $el = $(dynamicSelector); }
catch (e) {
  if (/unrecognized expression/.test(e.message)) { $el = $(); }
  else throw e;
}

When it happens

Trigger: Calling $("") or $(" ") when jQuery falls back to selector parsing; passing a malformed selector like $("div>>"), $("[attr='unterminated") or unsupported pseudo-syntax to $(), .find(), .filter(), .is(), .closest(); passing a non-string (e.g. null coerced to "null" syntax issues) where a selector is expected; building selectors by string concatenation where a variable is empty.

Common situations: Dynamically built selectors from empty form values or missing data attributes; third-party scripts/plugins calling $(element.dataset.target) where the attribute is missing; upgrading jQuery and a previously tolerated selector becomes invalid; typos in complex CSS selectors in templates.

Related errors

• Syntax error, unrecognized expression:
• Syntax error, unrecognized expression:
• Syntax error, unrecognized expression:
• Syntax error, unrecognized expression:
• Syntax error, unrecognized expression:

AI-assisted analysis of OrchardCMS/OrchardCore@4306c0717f (2026-09-13). Data as JSON: /api/errors/699ec168f2be4ab8. Report an issue: GitHub.

Appendix: source

Thrown at src/OrchardCore.Modules/OrchardCore.Resources/wwwroot/Vendor/jquery-3.6.0/jquery.js:1681

		val = fn && hasOwn.call( Expr.attrHandle, name.toLowerCase() ) ?
			fn( elem, name, !documentIsHTML ) :
			undefined;

	return val !== undefined ?
		val :
		support.attributes || !documentIsHTML ?
			elem.getAttribute( name ) :
			( val = elem.getAttributeNode( name ) ) && val.specified ?
				val.value :
				null;
};

Sizzle.escape = function( sel ) {
	return ( sel + "" ).replace( rcssescape, fcssescape );
};

Sizzle.error = function( msg ) {
	throw new Error( "Syntax error, unrecognized expression: " + msg );
};

/**
 * Document sorting and removing duplicates
 * @param {ArrayLike} results
 */
Sizzle.uniqueSort = function( results ) {
	var elem,
		duplicates = [],
		j = 0,
		i = 0;

	// Unless we *know* we can detect duplicates, assume their presence
	hasDuplicate = !support.detectDuplicates;
	sortInput = !support.sortStable && results.slice( 0 );
	results.sort( sortOrder );

	if ( hasDuplicate ) {

View on GitHub (pinned to 4306c0717f)