dotnet/AspNetCore.Docs · error · Error

Syntax error, unrecognized expression: ${msg}

Error message

Syntax error, unrecognized expression: ${msg}

What it means

jQuery's Sizzle selector engine throws via `Sizzle.error` when a selector string cannot be tokenized/parsed. The message is `'Syntax error, unrecognized expression: ' + msg`, surfacing the offending selector fragment.

Source

Thrown at aspnetcore/mvc/views/tag-helpers/th-components/samples/RazorPagesSample/wwwroot/lib/jquery/jquery.js:1463

	}

	var fn = Expr.attrHandle[ name.toLowerCase() ],
		// Don't get fooled by Object.prototype properties (jQuery #13807)
		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.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 c67a80103a)

Solutions

1. Escape meta-characters in dynamic values with `$.escapeSelector(value)` before interpolation.
2. Prefer attribute-value selectors with quotes: `$('[data-id="' + id + '"]')` instead of `$('#' + id)` when id may contain dots.
3. Validate the selector before use, or use `.find()` / `.filter()` with a function for dynamic matching.
4. Check for balanced brackets and valid syntax; log the selector to find the malformed fragment in the error message.

Example fix

// before
var $el = $('#' + userInput);  // fails if userInput has '.' or ':'

// after
var $el = $('[id="' + $.escapeSelector(userInput) + '"]');

function safeFind(selector, ctx) {
  try { return $(selector, ctx); }
  catch (e) {
    if (/Syntax error/.test(e.message)) {
      return ctx ? $(ctx).find(selector) : $();
    }
    throw e;
  }
}

function isValidSelector(selector) {
  try { document.createDocumentFragment().querySelector(selector); return true; }
  catch (e) { return false; }
}

try {
  return $(selector);
} catch (e) {
  if (/Syntax error/.test(e.message)) {
    console.warn('Bad selector:', selector);
    return $(); // empty collection
  }
  throw e;
}

When it happens

Trigger: Passing a malformed selector to any jQuery DOM method (`$()`, `.find()`, `.filter()`, `.on()` with delegation, etc.). Examples: unbalanced brackets `$('div[')`, leading/trailing special chars, invalid pseudo-classes, unescaped attribute values containing meta-characters.

Common situations: Dynamically building selectors from user input that contains `#`, `.`, `[`, `:`; attribute selectors with quotes/brackets in the value; typos in class/ID selectors; using a CSS selector where an HTML string was intended.

Related errors

• Syntax error, unrecognized expression: ${msg}
• Syntax error, unrecognized expression: ${msg}
• jQuery requires a window with a document
• Bootstrap's JavaScript requires jQuery
• Bootstrap's JavaScript requires jQuery version 1.9.1 or high

AI-assisted analysis of dotnet/AspNetCore.Docs@c67a80103a (2026-08-13). Data as JSON: /api/errors/dfdb15bf0fd4add1. Report an issue: GitHub.