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

Register custom helpers before compiling templates:

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 partials before use:

// 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

1. Compile template without errors
2. Render with sample data
3. Check output HTML is correct
4. 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