email-template-rendering

Development

Fix for Handlebars email template rendering issues in the notifications app. Use when: "Missing helper", template variables not rendering, partials not found, HTML escaping issues in emails. Only loads when working in apps/notifications/.

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Email Template Rendering Fixes

Problem

Handlebars templates for email notifications fail to render correctly, showing raw variables, missing helpers, or escaped HTML.

Trigger Conditions

Error: Missing helper: "formatDate"
Variables showing as {{variable}} in sent emails
Error: The partial X could not be found
HTML appearing escaped (<div> instead of <div>)
Working in apps/notifications/ directory

Solution

Issue 1: Missing Helpers

import Handlebars from 'handlebars';

// Register helpers BEFORE compiling templates
Handlebars.registerHelper('formatDate', (date: Date, format: string) => {
  return dayjs(date).format(format);
});

Handlebars.registerHelper('formatCurrency', (amount: number, currency: string) => {
  return new Intl.NumberFormat('en-US', {
    style: 'currency',
    currency: currency || 'USD',
  }).format(amount);
});

// Now compile
const template = Handlebars.compile(templateSource);

Issue 2: HTML Escaping

Use triple braces for unescaped HTML:

{{! WRONG - HTML will be escaped }}
<div>{{htmlContent}}</div>

{{! CORRECT - HTML renders as-is }}
<div>{{{htmlContent}}}</div>

Or use SafeString in helpers:

Handlebars.registerHelper('renderHtml', (html: string) => {
  return new Handlebars.SafeString(html);
});

Issue 3: Partials Not Found

// Register partial
Handlebars.registerPartial('header', headerTemplateSource);
Handlebars.registerPartial('footer', footerTemplateSource);

// Use in template
// {{> header}}
// ... content ...
// {{> footer}}

Issue 4: Async Data in Templates

Handlebars is synchronous. Resolve all data before rendering:

// WRONG
const template = Handlebars.compile(source);
const html = template({ user: await getUser() }); // ❌ Promise in template

// CORRECT
const user = await getUser();
const orders = await getOrders(user.id);
const template = Handlebars.compile(source);
const html = template({ user, orders }); // ✅ Resolved data

Verification

Compile template without errors
Render with sample data
Check output HTML is correct
Send test email and verify in email client

Notes

This skill only loads when working in apps/notifications/
Always precompile templates in production for performance
Test emails in multiple clients (Gmail, Outlook, Apple Mail)
Use inline CSS for email compatibility