VENTO

This is a minimal and experimental template engine inspired by other great engines like Nunjucks, Liquid, Mustache or EJS.

Why another template engine?

Because I couldn't find the "perfect" template engine for me (probably this one neither is). The issues I found in existing template engines:

Nunjucks

(It's my favorite template engine so far).

I like:
- I can invoke functions like {{ user.getName() }}.
- Very flexible, with many built-in filters and features
I don't like:
- It's not well maintained. The last version was released in Jun 2022. And the previous version in 2020.
- It's not async-friendly. For example, you have some tags to work with sync values (like for and if) and others for async values (like asyncEach and ifAysnc). Some features don't work in async contexts.
- To me, it's very uncomfortable to have to type the delimiters {% and %} all the time (especially the % character).
- By default, all variables are escaped, so you have to remember to use the safe filter everywhere. This is not very convenient for my use case (static site generators), where I can control all the content and the HTML generated.
- Some filters are too specific.

Liquid

I like:
- The support for async evaluation is less hacky than Nunjucks.
- The variables are not escaped by default, there's an escape filter for that.
I don't like:
- It's not possible to invoke functions in a liquid template. For example {{ user.getName() }} fails.
- It has the same problem as Nunjucks with the % character in the delimiters.

EJS/Eta

I like:
- It allows running any javascript code in the template.
I don't like:
- It has the same problem with the % character. And I don't like the opening and closing delimiters (<% and %>).
- Because it runs javascript, it's very verbose to do a simple forEach or if.

Mustache

I like:
- Very simple, everything is inside {{ and }}.
- The closing tag is {{/tagname}}, very nice!
I don't like:
- Perhaps too simple and the syntax can be a bit confusing.
- Partials. It's not easy to include them dynamically.
- The data context is a bit confusing to me.
- Very uncomfortable to work with filters.

What this new template engine has to offer?

First, let's take a look at this syntax example:

{{ if printName }}
  {{ await user.getName("full") |> toUpperCase }}
{{ /if }}

Everything is between {{ and }} tags. Unlike Nunjucks or Liquid, there's no distinction between tags {% tag %} and printing variables {{ var }}.
The closed tag is done by prepending the / character (like Mustache).
Async friendly.
Like EJS, you can use real JavaScript code everywhere. await user.getName("full") is real JS code that will be executed at runtime.
Filters are applied using the pipeline operator (|>). Note: this is not exactly like the last proposal for JavaScript, it's inspired by (the previous proposal that was rejected but it's way more simple and fits better for filters.
Filters can run prototype methods. In this example users.getName("full") returns a string, so the toUpperCase is a method of the String object. It's the same as users.getName("full").toUpperCase().

Getting started

This is a library for Deno. I'm planning to release an NPM version in the future.

First, you need to import the library and create an instance:

import vento from "https://deno.land/x/vento@v0.2.0/mod.ts";

const vto = vento({
  // Resolve the non-relative includes paths
  includes: "./path/to/includes",
});

There are different ways to load, compile and run a template. For example, you can use load to load and compile a template file and return it.

// Load and return a template
const template = vto.load("my-template.vto");

// Now you can use it passing the data
template({ title: "Hello world" });

Alternatively, you can load and run the template file in a single call:

vto.run("my-template.vto", { title: "Hello world" });

If the template code is not a file, you can run it directly:

vto.runString("<h1>{{ title }}</h1>", { title: "Hello world" });

Visual Studio Code Support

The Vento extension for VS Code enables syntax highlight and provides some useful snippets.

API

Print

Put a variable or expression between {{ }} to output the result.

Print a variable:
```
{{ name }}
```

Print the result of an expression:

{{ (name + " " + surname).toUpperCase() }}

Apply pipes with |>:

{{ name + " " + surname |> toUpperCase }}

Print conditionally
```
{{ name || "Unknown name" }}
```
Trim content (use - character next to the opening tag or previous to the closing tag to remove white space):
```
<h1>    {{- "Hello world" -}}    </h1>
```
This outputs <h1>Hello world</h1>.

For

Use for [value] of [collection] tag to iterate over arrays, dictionaries, numbers, strings, etc:

Arrays:

{{ for number of [1, 2, 3] }}
  {{ number }}
{{ /for }}

Objects:

{{ for person of [{name: "Óscar"}, {name: "Laura"}] }}
  {{ person.name }}
{{ /for }}

Numbers (to count from 1 to 10):

{{ for count of 10 }}
  {{ count }}
{{ /for }}

Strings (to split by letters):

{{ for letter of "Text" }}
  {{ letter }}
{{ /for }}

Use await for asynchronous iterators:

{{ for await item of getItems() }}
  {{ item }}
{{ /for }}

Use key, value to get the key of the iterator

{{ for key, value of { name: "Óscar", surname: "Otero" } }}
  Key: {{ key }}
  Value: {{ value }}
{{ /for }}

Apply filters to the collection before iterating it (in this example, filter the even numbers):
```
{{ for evenNumber of [1, 2, 3] |> filter((n) => n % 2 === 0) }}
  {{ evenNumber }}
{{ /for }}
```

If

Use if to test a condition. The syntax for the condition is the same as regular JavaScript if:

A simple condition:

{{ if user.is_active }}
  The user is active
{{ /if }}

If/else

{{ if user.is_active && user.is_logged }}
  The user is active and logged
{{ else }}
  The user is not active
{{ /if }}

If/else if

{{ if user.active }}
  The user is active
{{ else if user.logged }}
  The user is logged
{{ else }}
  The user is not active
{{ /if }}

The variables are exposed to the global scope. If the variable doesn't exist, an error is thrown:
```
{{ if non_existing_variable }}
  {{ non_existing_variable }}
{{ /if }}
```
This code returns the error ReferenceError: non_existing_variable is not defined. A way to avoid this in JavaScript:
```
{{ if typeof non_existing_variable !== "undefined" }}
  {{ non_existing_variable }}
{{ /if }}
```
But a more easy way is using the global object it, which contains all variables:
```
{{ if it.non_existing_variable }}
  {{ non_existing_variable }}
{{ /if }}
```

Include

To insert other templates in place. You can also include extra data.

Include a template
```
{{ include "filename.ven" }}
```
Include a template dynamically
```
{{ include `${filename}.ven` }}
```

Add extra data

{{ include `${filename}.ven` {name: "Value", name2: "Value2"} }}

Set

Allows to create or modify a variable.

Save a variable inline mode
```
{{ set message = "Hello world" }}
```

Save a variable block mode

{{ set message }}
  Hello world
{{ /set }}

Use pipes

{{ set message = "Hello world" |> toUpperCase }}

Use pipes in block mode

{{ set message |> toUpperCase }}
  Hello world
{{ /set }}

Comments

Use {{# to start a comment and #}} to end it. The commented code will be ignored by Vento and won't be printed.

{{# This is a commented code #}}

Raw

Use the {{ raw }} tag to disable the tag processing temporarily. This is useful for generating content (ej Nunjucks, Liquid, Mustache, etc) with conflicting syntax.

{{ raw }}
  In Handlebars, {{ this }} will be HTML-escaped, but
  {{{ that }}} will not.
{{ /raw }}

Arbitrary JavaScript code

You can insert any JavaScript code in the templates, that will be evaluated at runtime by starting the tag with > character. For example:

{{> console.log("Hello world") }}

Available filters

escape: To escape HTML code:
```
{{ "<h1>Hello world</h1>" |> escape }}
```
Any global function. For example:
```
{{ {name: "Óscar", surname: "Otero"} |> JSON.stringify }}
```
Because JSON.stringify is a function existing in the global scope, it's automatically used.
If the filter name is not registered and it's not in the global scope, Vento will try to execute it as an object property. For example:
```
{{ "https://example.com/data.json" |> await fetch |> await json |> JSON.stringify }}
```
- Note that fetch is a global function so Vento will execute it by passing the url as the argument.
- json is not in the global scope so it will be executed as a property of the response returned by fetch
- JSON.stringify is a global function
- The compiled code of this is equivalent to:
```
JSON.stringify(await (await fetch("https://example.com/data.json")).json());
```