Skip to main content
Version: 3.x.x

API Overview

Setting up Eta

Eta is exported as a class, so you must instantiate it before using it:

import { Eta } from "eta"
const eta = new Eta(options)

Passing in options is optional. You can find a list of all options here. Most users will need to pass in the views option, which is the path to your templates directory.

const eta = new Eta({ views: path.join(__dirname, "templates") })

Other common options include:

  • debug: Enables pretty-printing of runtime errors. Defaults to false.
  • cache: Whether to cache templates. Defaults to false.
  • autoEscape: Whether to automatically escape HTML in templates. Defaults to true.

Rendering Template Files


To render a template, use the render method:

const res = eta.render("templateName", { name: "Ben" })

The first argument is the name of the template, and the second argument is the data to pass to the template. The template name is relative to the views option passed in when instantiating Eta.

If you want to used named templates without resolving from the filesystem, name your templates with a leading @. Eta won't attempt to resolve those templates from the filesystem, and will instead look for them in the cache.


To render a template asynchronously, use the renderAsync method:

const res = await eta.renderAsync("templateName", { name: "Ben" })

The renderAsync method returns a promise, so you must use await or .then to get the result.

Rendering Strings

You can render a string as a template using the renderString method:

const res = eta.renderString("Hello <%= %>", { name: "Ben" })

Or render a string asynchronously using the renderStringAsync method:

const res = eta.renderStringAsync("Hello <%= await it.someFunction() %>", {
someFunction: () => Promise.resolve("Ben")

Defining Templates Programmatically

To define a template programmatically, use loadTemplate:

const headerPartial = `
<h1><%= it.title %></h1>

eta.loadTemplate("@header", headerPartial)

If your template isn't a file in the views directory, you must name it with a leading @ so that Eta knows not to resolve it from the filesystem.

The third argument to loadTemplate is an object of type {async: boolean} describing whether the template is async or not. By default, Eta will assume that the template is synchronous.

Common Use Cases

Custom Tags

You can change Eta's default tags by using the tags option:

const eta = new Eta({ tags: ["{{", "}}"] })

Auto-filtering Data

You can automatically filter all values by passing them through your own filter function:

const eta = new Eta({
autoFilter: true,
filterFunction: (val) => {
if (typeof val === "string") {
return val.toUpperCase()
return val

Getting rid of it

By default, Eta will store all data in the it variable. You can customize the name of this variable by using the varName option:

const eta = new Eta({ varName: "data" })

// "Hi <%= %>"

If you want to get rid of it entirely, you can use the useWith option:

const eta = new Eta({ useWith: true })
// "Hi <%= name %>"

This is generally considered to be bad practice, as it can lead to naming collisions / poor performance.

A better approach is to use the functionHeader configuration option:

const eta = new Eta({
functionHeader: "const, age=it.age"
// "Hi <%= name %>, our records show you are <%= age %> years old"

Customizing file handling

You can customize how Eta reads files by extending the Eta class and overriding the readFile and resolvePath methods:

class CustomEta extends Eta {
readFile = function (...) {...}

resolvePath = function (...) {...}