eta (η)

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Summary

Eta is a lightweight and blazing fast embedded JS templating engine that works inside Node, Deno, and the browser. Created by the developers of Squirrelly, it's written in TypeScript and emphasizes phenomenal performance, configurability, and low bundle size.

🌟 Features

• 📦 0 dependencies
• 💡 2.3KB minzipped; size restricted to <3KB forever with size-limit
• ⚡️ Written in TypeScript
• ✨ Deno support (+ Node and browser)
• 🚀 Super Fast
  • Check out these benchmarks
• 🔧 Configurable
  • Plugins, custom delimiters, caching
• 🔨 Powerful
  • Precompilation, partials, async
  • Layout support!
  • ExpressJS support out-of-the-box
• 🔥 Reliable
  • Better quotes/comments support
    • ex. <%= someval + "string %>" %> compiles correctly, while it fails with doT or EJS
  • Great error reporting
• ⚡️ Exports ES Modules as well as UMD
• 📝 Easy template syntax

Eta vs other template engines

Eta's syntax is very similar to EJS' (most templates should work with either engine), Eta has a similar API, and Eta and EJS share the same file-handling logic. Here are the differences between Eta and EJS:

• Eta is more lightweight. Eta weighs less than 2.5KB gzipped, while EJS is 4.4KB gzipped
• Eta compiles and renders templates much faster than EJS. Check out these benchmarks: https://rawgit.com/eta-dev/eta/master/browser-tests/benchmark.html
• Eta allows left whitespace control (with -), something that doesn't work in EJS because EJS uses - on the left side to indicate that the value shouldn't be escaped. Instead, Eta uses ~ to output a raw value
• Eta gives you more flexibility with delimeters -- you could set them to {{ and }}, for example, while with EJS this isn't possible
• Eta adds plugin support
• Comments in Eta use /* ... */ which allows commenting around template tags
• Eta parses strings correctly. Example: <%= "%>" %> works in Eta, while it breaks in EJS
• Eta exposes Typescript types and distributes a UMD build
• Eta supports custom tag-type indicators. Example: you could change <%= to <%*

Eta and doT.js both allow embedded JavaScript, and both have best-in-class performance when compared to other template engines (though Eta is slightly faster with HTML-escaped templates). Here are some of the differences between Eta and doT.js:

• Eta allows you to control how you strip preceding and trailing whitespace after tags.
• It's much simpler to set custom delimiters with Eta than doT -- you don't have to rewrite every configuration Regular Expression
• Eta supports plugins
• Eta supports async
• Eta parses strings and multi-line comments correctly. Example: <%= "%>" %> works in Eta, while the equivalent breaks in doT
• Eta exposes Typescript types and distributes a UMD build
• Eta supports runtime partials and file-handling.

Eta and Handlebars are very different in some ways -- Eta is an embedded template engine, while Handlebars is a logic-less template engine. Here some additional differences between Eta and Handlebars:

• Eta is more lightweight. Eta weighs less than 2.5KB gzipped, while Handlebars is ~22KB gzipped
• Eta compiles and renders templates much faster than Handlebars -- around 7x faster. Check out these benchmarks: https://ghcdn.rawgit.org/eta-dev/eta/master/browser-tests/benchmark.html
• Eta allows you to set custom delimiters
• Eta supports plugins
• Eta exposes Typescript types and distributes a UMD build
• Custom tag-type indicators. Example: you could change <%= to <%*
• With Eta, you don't need to register tons of helpers to do simple tasks like check if one value equals another value
• Note that Eta templates run as trusted code -- just like any other JavaScript you write.
  
  If you are running user-defined/created templates on your machine, server, site, etc., you probably should go with a tool built for that purpose, like Handlebars.

Template literals are a super useful tool, especially for shortening simple string concatenation. But writing complete templates using template literals can quickly get out of hand. Here's a comparison of Eta and template literals:

• Eta compiles templates into JavaScript functions that use string concatenation and have comparable performance with template literals
• Eta lets you control preceding and trailing whitespace around tags
• Eta gives you more flexibility with delimeters -- you could set them to {{ and }}, for example, or set them to ${ and } to mimic template literals
• Eta supports plugins
• Eta supports comments with /* ... */ syntax, just like in regular JavaScript. Template literals require you to stick a blank string after the comment: /* ... */"", which is much less readable
• To write conditionals inside template literals, you have to use the ternary operator. Add more conditions or nested conditionals, and it quickly becomes a nightmarish mess of ? ... : ... ? ... : .... Writing conditionals in Eta is much simpler and more readable
• Eta supports partials

Why Eta?

Simply put, Eta is super: super lightweight, super fast, super powerful, and super simple. Like with EJS, you don't have to worry about learning an entire new templating syntax. Just write JavaScript inside your templates.

Where did Eta's name come from?

"Eta" means tiny in Esperanto. Plus, it can be used as an acronym for all sorts of cool phrases: "ECMAScript Template Awesomeness", "Embedded Templating Alternative", etc....

Additionally, Eta is a letter of the Greek alphabet (it stands for all sorts of cool things in various mathematical fields, including efficiency) and is three letters long (perfect for a file extension).

Integrations

@shadowtime2000 created eta-vscode.

eslint-plugin-eta was created to provide an ESLint processor so you can lint your Eta templates.

An official Eta CLI exists called etajs-cli.

Currently there is no official Webpack integration but @clshortfuse shared the loader he uses:

{
  loader: 'html-loader',
  options: {
    preprocessor(content, loaderContext) {
      return eta.render(content, {}, { filename: loaderContext.resourcePath });
    },
  },
}

To operate with Eta templates in Node-RED: @ralphwetzel/node-red-contrib-eta

📜 Docs

We know nobody reads through the long and boring documentation in the ReadMe anyway, so head over to the documentation website:

📝 https://eta.js.org

📓 Examples

Simple Template

import * as Eta from "eta";
var myTemplate = "<p>My favorite kind of cake is: <%= it.favoriteCake %></p>";

Eta.render(myTemplate, { favoriteCake: "Chocolate!" });
// Returns: '<p>My favorite kind of cake is: Chocolate!</p>'

Conditionals

<% if(it.somevalue === 1) { %>
Display this
<% } else { %>
Display this instead
<% } %>

Loops

<ul>
<% it.users.forEach(function(user){ %>
<li><%= user.name %></li>
<% }) %>
</ul>

Partials

<%~ include('mypartial') %>

<%~ includeFile('./footer') %>

<%~ include('users', {users: it.users}) %>

✔️ Tests

Tests can be run with npm test. Multiple tests check that parsing, rendering, and compiling return expected results, formatting follows guidelines, and code coverage is at the expected level.

Resources

To be added

Projects using eta

• Docusaurus v2: open-source documentation framework that uses Eta to generate a SSR build
• swagger-typescript-api: Open source typescript api codegenerator from Swagger. Uses Eta as codegenerator by templates
• SmartDeno: SmartDeno is an easy to setup web template using Deno & Oak
• Add yours!

Contributors

Made with ❤ by @nebrelbug and all these wonderful contributors (emoji key):

Ben Gubler 💻 💬 📖 ⚠️	Clite Tailor 🤔 💻	Ioan CHIRIAC 💻 🤔	Craig Morten 💻	Rajan Tiwari 💡	shadowtime2000 💻 🤔 ⚠️	Hamza Hamidi 📖
Calum Knott 🤔	nhaef 💻	Gün 💻

This project follows the all-contributors specification. Contributions of any kind are welcome!

Credits

• Async support and file handling were added based on code from EJS, which is licensed under the Apache-2.0 license. Code was modified and refactored to some extent.
• Syntax and some parts of compilation are heavily based off EJS, Nunjucks, and doT.