ERB and Twig Cross-Reference for Front-End Development

February 26, 2019

Last Updated January 4, 2024

Your comprehensive cross-reference guide for Twig and ERB front-end view templates.

A version of this article appeared on viget.com

Two entire flowering plants, a yellow crocus (Crocus species) and a herb Paris (Paris quadrifolia). Colour nature print by A. Auer, c. 1853. Auer, Alois, 1813-1869. Public Domain Mark. Source: Wellcome Collection.

This post is geared towards developers who want to translate their Twig knowledge to ERB, or vice versa. If you’re only interested in one language or the other, check out Fundamental ERB for Front-End Development or Fundamental Twig for Front-End Development.

Contents

Introduction
Delimiters
Conditionals
Defining variables
Concatenation
Iteration (loops)
Inspecting data
Slicing
Trimming whitespace
Keyed values
Vertical inheritance
Using partials

Introduction

Twig and ERB are the two front-end templating languages I use most when developing websites. Here I document the ways each write just about everything to build views: comments, conditionals, variables and undefined variables, interpolation, loops and the loop index, slicing, handling whitespace, retrieving an keyed values, and templating with blocks and partials. If you’re familiar with one of Twig or ERB, use this as a cross-reference to translate your knowledge of the one language into the other. If you haven’t used either, this should get you up and running quickly. Read on to learn more about ERB and Twig, or skip ahead to the reference section.

What is Twig?

Twig is SensioLabs’ Django- / Jinja-like templating language for PHP. The recommended extension for Twig files is .twig, .<compiled_extension>.twig is useful, and .html —though inaccurate— is common in front-end templating. It’s used by SensioLabs’ Symfony; by Drupal 8, which is built on Symfony; and by Craft CMS.

Twig is a great language for building web front ends: it is full-featured without having more than one person could hope to learn, it reads fairly closely to English, and it has great official documentation. Twig is especially notable for its powerful support for complex inheritance across templates. Check out the use tag, the embed tag, and the block() function.

Twig even has Javascript implementations, making it easy to fit into projects built on the JS ecosystem. A quick overview to help you pick the one that best suits yours needs:

Mozilla’s Nunjucks is officially “jinja2 inspired” but it has [often followed Twig’s lead](https://github.com/mozilla/nunjucks/issues?utf8=✓&q=is%3Aissue is%3Aclosed twig ). If you use Gulp in your build tools, you can use gulp-nunjucks.
Twig.js is a popular JS port of Twig that sees more active development than Nunjucks does. It does not reach full parity with Twig (as of this writing Twig.js notably still has some bugs with Twig’s embed tag) but it currently comes closer than Nunjucks does and, since its goal is to duplicate Twig, it likely always will. The Twig.js Gulp plugin is gulp-twig.
Twing is a Twig engine for Node.js written in TypeScript which aims to always maintain complete parity with Twig. It is described as “a maintainability-first engine that passes 100% of the TwigPHP integration tests, is as close as possible to its code structure and expose an as-close-as-possible API.” Because Twing is able to essentially reuse much of Twig’s codebase, adding new features as they are merged into Twig is straightforward. Twing is the youngest of these projects… Twig users, show it your love! gulp-twing lets you use Twing with Gulp.

To learn Twig, read through the official documentation, and try things out in twigfiddle.

What is ERB?

ERB (Embedded Ruby) is a feature of Ruby that lets you —you guessed it!— embed Ruby in other files. ERB files have the extension .<compiled_extension>.erb. It is the language HAML and Slim are shorthand for. ERB is commonly used for templating Views in Rails apps.

Because it can do anything Ruby can do, it’s extremely powerful, has a much steeper learning curve than Twig, and can do a lot that isn’t relevant to front-end templating. There’s no cannonical ERB-for-front-end-developers documentation, and the Rails official documentation is immense and hard to dig through. Some resources if for learning ERB:

APIdock’s ActionView::Layouts and their documentation for the “included modules” listed under ActionView::Helpers (the UrlHelper’s link... and button_to methods are essential.
The APIdock TagHelper’s documentation for the content tag and tag methods are useful.
If you’re building forms familiarize yourself with the methods of the FormHelper, FormTagHelper, and FormOptionsHelper) (some will prefer the appearance of DevDocs — c.f. their ActionView and ActionView/Helpers documentation).
LaunchSchool’s Loops & Iterators is a good resource for understanding loops in Ruby.
Mix & Go’s How to use link_to in Rails is helpful for understanding link_to
RailsGuides’ Action View Overview and Layouts and Rendering in Rails cover Rails views in depth, with clear examples.

Delimiters

Comments

Inline comments

ERB: <%# … %>
erb
```
erb
<%# comment %>
```
```
erb
<%# comment %>
```
Twig: {# … #}
twig
```
twig
{# comment #}
```
```
twig
{# comment #}
```

Block comments

ERB: =begin…=end

the opening and closing tags must be at the start of the line

erb

erb
<%
=begin %>
                block comment
    (both lines of both the begin and end tags must be at the start of their lines)
<%
=end %>

erb
<%
=begin %>
                block comment
    (both lines of both the begin and end tags must be at the start of their lines)
<%
=end %>

not

erb

erb
                <%
                =begin %>
                not a comment
                <%
                =end %>

erb
                <%
                =begin %>
                not a comment
                <%
                =end %>

Twig: {# … #}

twig

twig
{#
block comment
#}

twig
{#
block comment
#}

twig

twig
not a comment {# block
comment #} not a comment

twig
not a comment {# block
comment #} not a comment

Outputting values

ERB: <%= … %>

erb

erb
<%= "print this" %> <%# output: `"print this"` %>
<%= 1 + 2 %>        <%# output: `3` %>

erb
<%= "print this" %> <%# output: `"print this"` %>
<%= 1 + 2 %>        <%# output: `3` %>

Twig: {{ }}

twig

twig
{{ "print this" }} {# output: `print this` #}
{{ 1 + 2 }}        {# output: `3` #}

twig
{{ "print this" }} {# output: `print this` #}
{{ 1 + 2 }}        {# output: `3` #}

Execution (Control Code)

ERB: <% … %>

erb

erb
<% if … do %> … <% end %>

erb
<% if … do %> … <% end %>

Twig: {% … %}

twig

twig
{% if … %} … {% endif %}

twig
{% if … %} … {% endif %}

Conditionals

Single-statement conditionals

ERB: if and unless

erb

erb
<%= 2 if true %> <%# output: `2` %>
<%= 2 if false %> <%# output: `nil` %>
<%= 2 unless true %> <%# output: `nil` %>
<%= 2 unless false %> <%# output: `2` %>

erb
<%= 2 if true %> <%# output: `2` %>
<%= 2 if false %> <%# output: `nil` %>
<%= 2 unless true %> <%# output: `nil` %>
<%= 2 unless false %> <%# output: `2` %>

Multi-statement conditionals

ERB: if…elsif…end

erb

erb
<%# assuming x, y, z, and n are defined %>
<% if x %>
    y
<% elsif z == n %> <%# note the spelling of elsif %>
    0
<% else %>
    1
<% end %>

erb
<%# assuming x, y, z, and n are defined %>
<% if x %>
    y
<% elsif z == n %> <%# note the spelling of elsif %>
    0
<% else %>
    1
<% end %>

Twig: if…elseif…endif

twig

twig
{% if x %}
    y
{% elseif z == n %}{# note the spelling of elseif #}
    0
{% else %}
    1
{% endif %}

twig
{% if x %}
    y
{% elseif z == n %}{# note the spelling of elseif #}
    0
{% else %}
    1
{% endif %}

Conditionals with logical operators

Both ERB and Twig support “condition ? iftrue : iffalse”, and “ifselftrue ?: otherwise”.

ERB. Note that the “then” case : must be provided

erb

erb
<%# assuming x, y, z, and n are defined %>
<%# if x then y %>
<%# omitting the "else" will throw an error #>
<%= x ? y : '' %>
<%# if x is true, y. otherwise, if z equals n then 0. otherwise 1 %>
<%= x ? y : z == n ? 0 : 1 %>
<%# ternary operator: x if x is true, otherwise y %>
<%= x ?: y %>

erb
<%# assuming x, y, z, and n are defined %>
<%# if x then y %>
<%# omitting the "else" will throw an error #>
<%= x ? y : '' %>
<%# if x is true, y. otherwise, if z equals n then 0. otherwise 1 %>
<%= x ? y : z == n ? 0 : 1 %>
<%# ternary operator: x if x is true, otherwise y %>
<%= x ?: y %>

Twig

twig

twig
{# assuming x, y, z, and n are defined and/or Twig's strict variables option is turned off #}
{# if x then y #}
{{ x ? y }}
{# if x is true, y. otherwise, if z equals n then 0. otherwise 1 #}
{{ x ? y : z == n ? 0 : 1 }}
{# ternary operator: x if x is true, otherwise y #}
{{ x ?: y }}

twig
{# assuming x, y, z, and n are defined and/or Twig's strict variables option is turned off #}
{# if x then y #}
{{ x ? y }}
{# if x is true, y. otherwise, if z equals n then 0. otherwise 1 #}
{{ x ? y : z == n ? 0 : 1 }}
{# ternary operator: x if x is true, otherwise y #}
{{ x ?: y }}

Truth and falsity of zero in Boolean contexts

ERB: 0 is True in Boolean contexts

erb

erb
<%= false ? 'truthy' : 'falsy' %> <%# output: `"falsy"` %>
<%= 0 ? 'truthy' : 'falsy' %>     <%# output: `"truthy"` %>

erb
<%= false ? 'truthy' : 'falsy' %> <%# output: `"falsy"` %>
<%= 0 ? 'truthy' : 'falsy' %>     <%# output: `"truthy"` %>

Twig: as in PHP generally, 0 is False in Boolean contexts

twig

twig
{{ false ? 'truthy' : 'falsy' }} {# output: `falsy` #}
{{ 0 ? 'truthy' : 'falsy' }}     {# output: `falsy` #}

twig
{{ false ? 'truthy' : 'falsy' }} {# output: `falsy` #}
{{ 0 ? 'truthy' : 'falsy' }}     {# output: `falsy` #}

Defining variables

ERB: =

erb

erb
<% var = 1 %>
<% anotherVar = 0 %>
<% falseVar = false %>
<%= 2 if var %>          <%# output: `2` %>
<%= 2 if anotherVar %>   <%# output: `2` %>
<%= 2 if falseVar %>     <%# output: `` %>
<%= 2 unless falseVar %> <%# output: `2` %>

erb
<% var = 1 %>
<% anotherVar = 0 %>
<% falseVar = false %>
<%= 2 if var %>          <%# output: `2` %>
<%= 2 if anotherVar %>   <%# output: `2` %>
<%= 2 if falseVar %>     <%# output: `` %>
<%= 2 unless falseVar %> <%# output: `2` %>

Twig: set

twig

twig
{% set var = 1 %}
{% set anotherVar = 0 %}
{% set falseVar = false %}
{{ var ? 2 }}           {# output: `2` #}
{{ anotherVar ? 2 }}    {# output: null - Twig, unlike PHP, equates 0 with falsehood #}
{{ falseVar ? '' : 2 }} {# output `2` #}

twig
{% set var = 1 %}
{% set anotherVar = 0 %}
{% set falseVar = false %}
{{ var ? 2 }}           {# output: `2` #}
{{ anotherVar ? 2 }}    {# output: null - Twig, unlike PHP, equates 0 with falsehood #}
{{ falseVar ? '' : 2 }} {# output `2` #}

Twig can define multiple variables in a single call — just keep in mind that developers not used to this might overlook the multiple declarations!

twig

twig
{% set x, y, z = 1, 2, 3 %}

twig
{% set x, y, z = 1, 2, 3 %}

(A value must be explicitly provided for each variable: {% set x, y = 1 %} will error.)

Line breaks within a variable’s value

ERB: multi-line blocks of markup can stored in an identifier with content_for x do…end

erb

erb
<% content_for longVar do %>
  <div>
    …
  </div>
<% end %>
<%= content_for(longVar) %>

erb
<% content_for longVar do %>
  <div>
    …
  </div>
<% end %>
<%= content_for(longVar) %>

Note: content_for is additive: each time you provide content for a given variable, that content is appeneded to what was there already. To use content_for to overwrite a global variable, use the flush: true option:

erb

erb
<% content_for refreshedVar do %>
    a
<% end %>
<% content_for refreshedVar, flush: true do %>
    b
<% end %>

erb
<% content_for refreshedVar do %>
    a
<% end %>
<% content_for refreshedVar, flush: true do %>
    b
<% end %>

Twig: use the set tag’s form set x…endset to capture chunks of text

twig

twig
{% set longVar %}
  <div>
    …
  </div>
{% endset %}
{{ longVar }}

twig
{% set longVar %}
  <div>
    …
  </div>
{% endset %}
{{ longVar }}

Dealing with undefined variables

ERB:

defined?()

erb

erb
<%# output: the content if `var` is defined %>
<% if defined?(var) %>
  …
<% end %>
<%# output: `var` if `var` is defined, otherwise `fallback` %>
<%= defined?(var) ? var : fallback %>

erb
<%# output: the content if `var` is defined %>
<% if defined?(var) %>
  …
<% end %>
<%# output: `var` if `var` is defined, otherwise `fallback` %>
<%= defined?(var) ? var : fallback %>

||=, the OR Equal operator

erb

erb
<%# output: `var` if it is defined and not nil and not false, otherwise `fallback` %>
<% var ||= fallback %>
<%
=begin %> common front-end use cases:
1. output a variable only if it is defined
<%
=end %>
<% var ||= nil %>
<%# set a variable with a fallback %>
<% x = y ||= nil %>

erb
<%# output: `var` if it is defined and not nil and not false, otherwise `fallback` %>
<% var ||= fallback %>
<%
=begin %> common front-end use cases:
1. output a variable only if it is defined
<%
=end %>
<% var ||= nil %>
<%# set a variable with a fallback %>
<% x = y ||= nil %>

Twig:

is defined

Especially useful when Twig’s strict variables option is turned on, in which case referring to an undefined variable will throw an error.

twig

twig
{# output: Twig_Error_Runtime: Variable "x" does not exist. #}
{{ x }}
{# output: the content if var is defined #}
{% if var is defined %}
  …
{% endif %}
{# output: `advance` if var is defined, otherwise `fallback` #}
{{ var is defined ? advance : fallback }}

twig
{# output: Twig_Error_Runtime: Variable "x" does not exist. #}
{{ x }}
{# output: the content if var is defined #}
{% if var is defined %}
  …
{% endif %}
{# output: `advance` if var is defined, otherwise `fallback` #}
{{ var is defined ? advance : fallback }}

??, the null coalescing operator

twig

twig
{# output: `var` if it is defined and not null, otherwise `fallback` #}
{{ var ?? fallback }}
{# common use cases:
1. output a variable only if it is defined #}
{{ var ?? null }}
{# set a variable with a fallback #}
{% set x = y ?? null %}

twig
{# output: `var` if it is defined and not null, otherwise `fallback` #}
{{ var ?? fallback }}
{# common use cases:
1. output a variable only if it is defined #}
{{ var ?? null }}
{# set a variable with a fallback #}
{% set x = y ?? null %}

Variable interpolation

ERB: #{var}

erb

erb
<% x = 1 %>
<%= "this is interpolated: #{x}" %><%# output: `this is interpolated: 1` %>

erb
<% x = 1 %>
<%= "this is interpolated: #{x}" %><%# output: `this is interpolated: 1` %>

Twig: #{var}

twig

twig
{% set x = 1 %}
{{ "this is interpolated #{x}" }}{# output: `this is interpolated: 1` #}

twig
{% set x = 1 %}
{{ "this is interpolated #{x}" }}{# output: `this is interpolated: 1` #}

Concatenation

ERB: + (plus). Note that to concatenate a string and a number in Ruby, the number must be converted to a string.

erb

erb
<% string_variable = 'world' %>
<% number_variable = 2 %>
<%= 'hello ' + string_variable %>   <%# output: `"hello world"` %>
<%= "example #{number_variable}" %> <%# output: `"example 2"` %>
<%= 'example ' + 3.to_s %>          <%# output: `"example 3"` %>

erb
<% string_variable = 'world' %>
<% number_variable = 2 %>
<%= 'hello ' + string_variable %>   <%# output: `"hello world"` %>
<%= "example #{number_variable}" %> <%# output: `"example 2"` %>
<%= 'example ' + 3.to_s %>          <%# output: `"example 3"` %>

Twig: ~ (tilde). Note that strings and numbers can be freely concatenated.

twig

twig
{% set string_variable = 'world' %}
{% set number_variable = 2 %}
{{ 'hello ' ~ string_variable }}   {# output: `hello world` #}
{{ "example #{number_variable}" }} {# output: `example 2` #}
{{ 'example ' ~ 3 }}               {# output: `example 3` #}

twig
{% set string_variable = 'world' %}
{% set number_variable = 2 %}
{{ 'hello ' ~ string_variable }}   {# output: `hello world` #}
{{ "example #{number_variable}" }} {# output: `example 2` #}
{{ 'example ' ~ 3 }}               {# output: `example 3` #}

Iteration (loops)

Iterating over items

ERB: n.each do |i|…end

erb

erb
<% items = ['a', 'b', 'c'] %>
<%# output: `...` %>
<% [0..items.length].each do %>.<% end %>
<%# output: `a b c ` %>
<% items.each do |item| %>
    <%= item %>
<% end %>

erb
<% items = ['a', 'b', 'c'] %>
<%# output: `...` %>
<% [0..items.length].each do %>.<% end %>
<%# output: `a b c ` %>
<% items.each do |item| %>
    <%= item %>
<% end %>

Twig: for i in n…endfor

twig

twig
{% set items = ['a','b','c'] %}
{# output: `...` #}
{% for i in 0..items.length %}.{% endfor %}
{# output: `a b c ` #}
{% for item in items %}
    {{item}}
{% endfor %}

twig
{% set items = ['a','b','c'] %}
{# output: `...` #}
{% for i in 0..items.length %}.{% endfor %}
{# output: `a b c ` #}
{% for item in items %}
    {{item}}
{% endfor %}

Using the loop index, 0-indexed

ERB:

n.each_with_index do |i, index|…end

erb

erb
<%# output: `0. a 1. b 2. c ` %>
<% items = ['a', 'b', 'c'] %>
<% items.each_with_index do |item,index| %>
    <%= index %>. <%= item %>
<% end %>

erb
<%# output: `0. a 1. b 2. c ` %>
<% items = ['a', 'b', 'c'] %>
<% items.each_with_index do |item,index| %>
    <%= index %>. <%= item %>
<% end %>

n.times do |i|…end

erb

erb
<%# output: `0 1 2 3 4 5 6 7 8 9` %>
<% 10.times do |i| %><%= i %> <% end %>

erb
<%# output: `0 1 2 3 4 5 6 7 8 9` %>
<% 10.times do |i| %><%= i %> <% end %>

Twig: loop.index0

twig

twig
{% for item in items %}
    {{loop.index0}}. {{item}}
{% endfor %}

twig
{% for item in items %}
    {{loop.index0}}. {{item}}
{% endfor %}

Using the loop index, 1-indexed

ERB:

.each_with_index’s index is always 0-indexed, so add 1

erb

erb
<% items.each_with_index do |item,index| %>
    <%= index + 1 %>. <%= item %>
<% end %>

erb
<% items.each_with_index do |item,index| %>
    <%= index + 1 %>. <%= item %>
<% end %>

n.times do |i|…end

erb

erb
<%# output: `1 2 3 4 5 6 7 8 9 10 ` %>
<% 10.times do |i| %><%= i %> <% end %>

erb
<%# output: `1 2 3 4 5 6 7 8 9 10 ` %>
<% 10.times do |i| %><%= i %> <% end %>

Twig: loop.index

twig

twig
{% for item in items %}
    {{loop.index}}. {{item}}
{% endfor %}

twig
{% for item in items %}
    {{loop.index}}. {{item}}
{% endfor %}

Iterating a certain number of times

ERB: n.times do |i|…end

erb

erb
<% n = 3 %>
<%# output: `...` %>
<% n.times do %>.<% end %>
<%# output: `1 2 3 ` %>
<% n.times do |i| %>
    <%= i %>
<% end %>

erb
<% n = 3 %>
<%# output: `...` %>
<% n.times do %>.<% end %>
<%# output: `1 2 3 ` %>
<% n.times do |i| %>
    <%= i %>
<% end %>

Twig: for i in n…endfor

twig

twig
{% set items = ['a','b','c'] %}
{# output: `...` #}
{% for i in 0..items.length %}.{% endfor %}
{# output: `a b c ` #}
{% for item in items %}
    {{item}}
{% endfor %}

twig
{% set items = ['a','b','c'] %}
{# output: `...` #}
{% for i in 0..items.length %}.{% endfor %}
{# output: `a b c ` #}
{% for item in items %}
    {{item}}
{% endfor %}

Inspecting data

ERB: several options for formatting an object’s data, notably: simply outputting, .inspecting, and debug()ing. For basic data-checking purposes in a view, the essential difference is debug() returns YAML while inspect and printing return strings.
erb
```
erb
<%# for some object `posts` %>
<%= posts %>
<%= posts.inspect %>
<%= debug(posts) %>
```
```
erb
<%# for some object `posts` %>
<%= posts %>
<%= posts.inspect %>
<%= debug(posts) %>
```
Twig:
- The |json_encode() filter formats an object’s data.
  twig
```
twig
{# for some object `posts` #}
{{ posts|json_encode }}
```
```
twig
{# for some object `posts` #}
{{ posts|json_encode }}
```
- The dump() function outputs information about a variable.
  twig
```
twig
{# for some object `posts` #}
{{ dump(posts) }}
```
```
twig
{# for some object `posts` #}
{{ dump(posts) }}
```
  Note: dump must be enabled. Some implementations make it available out of the box (for example, Craft CMS in dev mode).

Slicing

ERB: .slice(index), .slice(start,count)

erb

erb
<%= [1,2,3,4].slice(1) %>   <%# output: `2` %>
<%= [1,2,3,4].slice(1,2) %> <%# output: `[2,3]` %>

erb
<%= [1,2,3,4].slice(1) %>   <%# output: `2` %>
<%= [1,2,3,4].slice(1,2) %> <%# output: `[2,3]` %>

Twig: |slice(start,count) or [start:count]

twig

twig
{{ [1,2,3,4]|slice(1) }}   {# output: `Array` #}
{{ [1,2,3,4]|slice(1,2) }} {# output: `Array` #}

twig
{{ [1,2,3,4]|slice(1) }}   {# output: `Array` #}
{{ [1,2,3,4]|slice(1,2) }} {# output: `Array` #}

Note: The output of the above Twig examples is Array, because in Twig the output of {{ [anArray] }} is Array. If you need to print an array, use |json_encode:

twig

twig
{{ [1,2,3,4]|slice(1)|json_encode() }}   {# output: `[2,3,4]` #}
{{ [1,2,3,4]|slice(1,2)|json_encode() }} {# output: `[2,3]` #}

twig
{{ [1,2,3,4]|slice(1)|json_encode() }}   {# output: `[2,3,4]` #}
{{ [1,2,3,4]|slice(1,2)|json_encode() }} {# output: `[2,3]` #}

In execution, no special steps are necessary:

twig

twig
{% set myArray = [1,2,3,4] %}
…

twig
{% set myArray = [1,2,3,4] %}
…

Shorthand to slice the first `count` items

ERB: .take(count) or .first(count)

erb

erb
<%= [1,2,3,4].take(2) %>  <%# output: `[1,2]` %>
<%= [1,2,3,4].first(2) %> <%# output: `[1,2]` %>

erb
<%= [1,2,3,4].take(2) %>  <%# output: `[1,2]` %>
<%= [1,2,3,4].first(2) %> <%# output: `[1,2]` %>

Twig: [:count]

twig

twig
{{ [1,2,3,4][:2]|json_encode() }} {# output: `[1,2]` #}

twig
{{ [1,2,3,4][:2]|json_encode() }} {# output: `[1,2]` #}

Shorthand for everything after the `start` item

Twig: [start:]

twig

twig
{{ [1,2,3,4][2:]|json_encode() }} {# output: `[3,4]` #}

twig
{{ [1,2,3,4][2:]|json_encode() }} {# output: `[3,4]` #}

Trimming whitespace

ERB

If trim_mode is set to -, a - in the closing erb tag will trim trailing whitespace:

erb

erb
<% something -%>
1
<%= something_else -%>
2
<% another_thing %>

erb
<% something -%>
1
<%= something_else -%>
2
<% another_thing %>

is equivalent to

erb

erb
<% something %>1
<%= something_else %>2
<% another_thing %>

erb
<% something %>1
<%= something_else %>2
<% another_thing %>

Twig

Trim leading or trailing whitespace by adding a - inside in an opening or close delimiter, respectively:

twig

twig
{% something -%}
1
{%- something_else -%}
2
{%- last_thing %}

twig
{% something -%}
1
{%- something_else -%}
2
{%- last_thing %}

is equivalent to

twig

twig
{% something %}1{% something_else %}2{% last_thing %}

twig
{% something %}1{% something_else %}2{% last_thing %}

Trimming space between HTML elements

Twig

Twig doesn’t care what language you are compiling to, but it does provide a special spaceless tag for use with HTML.

twig

twig
{% spaceless %}
  <div>…</div>
  <span>…</span>
{% endspaceless %}

twig
{% spaceless %}
  <div>…</div>
  <span>…</span>
{% endspaceless %}

is equivalent to

twig

twig
<div>…</div><span>…</span>

twig
<div>…</div><span>…</span>

Note that this spaceless has limited powers:

it isn’t recursive

twig

twig
{% spaceless %}
  <div>
    <div>
      …
    </div>
  <div>
  <span>…</span>
{% endspaceless %}

twig
{% spaceless %}
  <div>
    <div>
      …
    </div>
  <div>
  <span>…</span>
{% endspaceless %}

is equivalent to

twig

twig
<div><div>
    …
  </div><div><span>…</span>

twig
<div><div>
    …
  </div><div><span>…</span>

and content between HTML tags will disrupt it

twig

twig
{% spaceless %}
  <div>…</div>
  sorry, spaceless
  <span>…</span>
{% endspaceless %}

twig
{% spaceless %}
  <div>…</div>
  sorry, spaceless
  <span>…</span>
{% endspaceless %}

is equivalent to

twig

twig
<div>…</div>
  sorry, spaceless
  <span>…</span>

twig
<div>…</div>
  sorry, spaceless
  <span>…</span>

Keyed values

ERB:

Use a Symbol :property to look up an operation on a Hash:

erb

erb
<% myHash = {hello: 'world'} %>
<%= myHash[:hello] %> <%# output: "world" %>

erb
<% myHash = {hello: 'world'} %>
<%= myHash[:hello] %> <%# output: "world" %>

Twig:

Use dot notation or subscript syntax to access attributes of a variable:

twig

twig
{% set myVar = {hello: 'world'} %}
{{ myVar.hello }} {# output: world #}
{{ myVar['hello'] }} {# output: world #}

twig
{% set myVar = {hello: 'world'} %}
{{ myVar.hello }} {# output: world #}
{{ myVar['hello'] }} {# output: world #}

Vertical inheritance

For a layout file that pulls in page:

ERB: content_for in child, yield in parent

layouts/layout.html.erb

erb

erb
<%= yield :myBlock %>

erb
<%= yield :myBlock %>

views/page.html.erb

erb

erb
<% content_for :myBlock do %>
    the content
<% end %>

erb
<% content_for :myBlock do %>
    the content
<% end %>

Twig: block + extends in child, block in parent.

layout.html.twig

twig

twig
{% block myBlock '' %}
{# or #}
{% block myBlock %}{% endblock %}
{# or #}
{% block myBlock %}{% endblock myBlock %}

twig
{% block myBlock '' %}
{# or #}
{% block myBlock %}{% endblock %}
{# or #}
{% block myBlock %}{% endblock myBlock %}

page.html.twig

twig

twig
{% extends 'layout.html.twig' %}
{% block myBlock %}
    the content
{% endblock %}

twig
{% extends 'layout.html.twig' %}
{% block myBlock %}
    the content
{% endblock %}

or if all the content is a variable x, page.html.twig

twig

twig
{% extends 'layout.html.twig' %}
{% block myBlock x %}

twig
{% extends 'layout.html.twig' %}
{% block myBlock x %}

or if all the content is a single string, page.html.twig

twig

twig
{% extends 'layout.html.twig' %}
{% block myBlock "#{x} content" %}
{# or #}
{% extends 'layout.html.twig' %}
{% block myBlock x ~ "content" %}

twig
{% extends 'layout.html.twig' %}
{% block myBlock "#{x} content" %}
{# or #}
{% extends 'layout.html.twig' %}
{% block myBlock x ~ "content" %}

or if all the content is a single literal string, page.html.twig

twig

twig
{% extends 'layout.html.twig' %}
{% block myBlock 'the content' %}
{# or #}
{% block myBlock "the content" %}

twig
{% extends 'layout.html.twig' %}
{% block myBlock 'the content' %}
{# or #}
{% block myBlock "the content" %}

Vertical inheritance with default content in the parent

ERB

layouts/layout.html.erb

erb

erb
<% if content_for?(:my_content) %>
    <%= yield :my_content %>
<% else %>
    default content
<% end %>

erb
<% if content_for?(:my_content) %>
    <%= yield :my_content %>
<% else %>
    default content
<% end %>

views/page.html.erb

erb

erb
<% content_for :my_content do %>
    the content
<% end %>

erb
<% content_for :my_content do %>
    the content
<% end %>

Twig

main.html.twig

twig

twig
{% block content %}
    default content
    {% block sub_content '' %}
{% endblock %}

twig
{% block content %}
    default content
    {% block sub_content '' %}
{% endblock %}

override-content.html.twig

twig

twig
{% extends 'main.html.twig' %}
{% block content %}
    the content
{% endblock %}

twig
{% extends 'main.html.twig' %}
{% block content %}
    the content
{% endblock %}

Result of override-content.html.twig:

default content

default content

override-subcontent.html.twig

twig

twig
{% extends 'main.html.twig' %}
{% block subcontent %}
    the sub-content
{% endblock %}

twig
{% extends 'main.html.twig' %}
{% block subcontent %}
    the sub-content
{% endblock %}

Result of override-subcontent.html.twig:

default content
  the sub-content

default content
  the sub-content

Using partials

ERB:

render will output the contents of another file

erb

erb
<%= render 'path/to/x' %>

erb
<%= render 'path/to/x' %>

To pass values to the rendered file, define them:

erb

erb
<% a = 1 %>
<% b = 2 %>
<%= render 'path/to/x', a:a, b:b %> <%# in path/to/x a=1 and b=2 %>

erb
<% a = 1 %>
<% b = 2 %>
<%= render 'path/to/x', a:a, b:b %> <%# in path/to/x a=1 and b=2 %>

If the rendered file expects different variable names, use those:

erb

erb
<% a = 1 %>
<% b = 2 %>
<%= render 'path/to/x', y:a, z:b %> <%# in path/to/x y=1 and z=2 %>

erb
<% a = 1 %>
<% b = 2 %>
<%= render 'path/to/x', y:a, z:b %> <%# in path/to/x y=1 and z=2 %>

Twig:

include tag

twig

twig
{% include 'path/to/x' %}

twig
{% include 'path/to/x' %}

include function

twig

twig
{{ include('path/to/x') }}

twig
{{ include('path/to/x') }}

The include tag passes the entire parent context to the included file by default:

twig

twig
{% set a = 1 %}
{% set b = 2 %}
{% include 'path/to/x' %} {# in path/to/x a=1 and b=2 #}

twig
{% set a = 1 %}
{% set b = 2 %}
{% include 'path/to/x' %} {# in path/to/x a=1 and b=2 #}

To pass only certain data, use include with only:

twig

twig
{% set a = 1 %}
{% set b = 2 %}
{% include 'path/to/x' with {a:a} only %}
{# in path/to/x a=1 and b does not exist #}

twig
{% set a = 1 %}
{% set b = 2 %}
{% include 'path/to/x' with {a:a} only %}
{# in path/to/x a=1 and b does not exist #}

Rename variables in the with (can be combined with only):

twig

twig
{% set a = 1 %}
{% include 'path/to/x' with {y:a} %} {# in path/to/x a=1 and y=1 #}
{% include 'path/to/z' with {y:a} only %}
{# in path/to/z y=1 and a does not exist  #}

twig
{% set a = 1 %}
{% include 'path/to/x' with {y:a} %} {# in path/to/x a=1 and y=1 #}
{% include 'path/to/z' with {y:a} only %}
{# in path/to/z y=1 and a does not exist  #}

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