Common Error Messages

Here are some common error messages you may encounter when using complex template expressions:

“Template syntax error: Expected quoted attribute value” — Complex expression in attribute without quotes
“Template syntax error: Unexpected token” — HTML non-compliant character (like <) in text node, or malformed expression
“‘this’ is not allowed in template expressions” — Using this keyword
“‘new’ operator is not allowed in template expressions” — Using new operator
“Function declarations are not allowed in template expressions” — Using function declaration instead of arrow function
“Arrow functions with block bodies are not allowed” — Using block body in arrow function
“Assignment operators are not allowed outside arrow functions” — Assignment outside arrow function
“Update operators are not allowed outside arrow functions” — Update operator (++, --) outside arrow function

HTML Compliance Errors in Text Nodes

Using HTML non-compliant characters like < in text node expressions will cause parsing errors.

1<!-- ❌ Error: < character in text node -->
2<div>{age < 18 ? 'Minor' : 'Adult'}</div>
3<!-- Error: Template syntax error: Unexpected token -->
4
5<!-- ❌ Error: <= operator in text node -->
6<div>{count <= 10 ? 'Low' : 'High'}</div>
7<!-- Error: Template syntax error: Unexpected token -->
8
9<!-- ✅ Valid - use HTML-compliant alternatives -->
10<div>{age >= 18 ? 'Adult' : 'Minor'}</div>
11<div>{count > 10 ? 'High' : 'Low'}</div>

Syntax Errors in Expressions

Malformed expressions will result in syntax errors.

1<!-- ❌ Error: Missing closing parenthesis -->
2<div>{formatCurrency(price}</div>
3<!-- Error: Expected closing parenthesis -->
4
5<!-- ❌ Error: Missing closing brace in template literal -->
6<div>{`Hello ${name`}</div>
7<!-- Error: Expected closing brace in template literal -->
8
9<!-- ❌ Error: Invalid operator usage -->
10<div>{foo && && bar}</div>
11<!-- Error: Unexpected token -->
12
13<!-- ✅ Valid expressions -->
14<div>{formatCurrency(price)}</div>
15<div>{`Hello ${name}`}</div>
16<div>{foo && bar}</div>

1import { LightningElement } from "lwc";
2
3export default class SyntaxErrorsComponent extends LightningElement {
4  price = 99.99;
5  name = "World";
6  foo = true;
7  bar = "value";
8
9  formatCurrency(price) {
10    return `$${price.toFixed(2)}`;
11  }
12}

Release Preview

This release is in preview. Features described here don't become generally available until the latest general availability date that Salesforce announces for this release. Before then, and where features are noted as beta, pilot, or developer preview, we can't guarantee general availability within any particular time frame or at all. Make your purchase decisions only on the basis of generally available products and features.