Parsing #3 — Building a Template Engine

Template engines replace placeholders with data — Handlebars, Mustache, even React's JSX compiles to something similar. This article builds a minimal template engine that handles variable interpolation, loops, and conditionals using regex.

Prerequisites: JS Foundations #8 — Template Literals

1. Simple Variable Replacement — {{ var }}

2. Conditionals — {{#if}} and {{/if}}

3. Loops — {{#each}} and {{/each}}

4. Full Engine — if, unless, each, and variables

Combining everything into one function:

5. Escaping — Preventing HTML Injection

Always escape user-supplied data in templates:

Key Takeaways

• Regex \{\{\s*([\w.]+)\s*\}\} matches template variables with optional dot notation.
• Block helpers (#each, #if, #unless) need regex that handles nested content (basic [\s\S]*?).
• Dot-notation path resolution: split by ., reduce over the data object.
• Always escape user data in templates with {{{ }}} reserved for trusted HTML.
• This pattern scales to handlebars/mustache/liquid — the regex engine just gets more sophisticated.

Next: V8 #1 — JIT Compilation & Hidden Classes — how V8's Ignition and TurboFan make JavaScript fast.