ActiveSupport

The ActiveSupport filter provides JavaScript equivalents for common Rails ActiveSupport core extensions. These methods are frequently used in Rails templates and views.

Supported Methods

Object Methods

blank?

Returns true if the object is null, empty, or a blank string.

name.blank?

name == null || name.length === 0 || name === ""

present?

The opposite of blank? - returns true if the object has meaningful content.

user.email.present?

user.email != null && user.email.length != 0 && user.email != ""

presence

Returns the object if it’s present?, otherwise returns null.

name.presence || "Anonymous"

(name != null && name.length != 0 && name != "" ? name : null) || "Anonymous"

try

Calls a method on the receiver, returning null if the receiver is null or undefined. Uses JavaScript optional chaining (?.).

user.try(:name)
user.try(:fetch, :key)

user?.name()
user?.fetch("key")

in?

Checks if the object is included in a collection. The inverse of include?.

status.in?(["active", "pending"])

["active", "pending"].includes(status)

String Methods

squish

Removes leading/trailing whitespace and collapses internal whitespace to single spaces.

"  hello   world  ".squish

"  hello   world  ".trim().replace(/\s+/g, " ")

truncate

Truncates a string to a specified length, adding an omission marker (default: "...").

title.truncate(50)
description.truncate(100, omission: "…")

title.length > 50 ? title.slice(0, 47) + "..." : title
description.length > 100 ? description.slice(0, 99) + "…" : description

Array Methods

to_sentence

Converts an array to a comma-separated sentence with “and” before the last element.

["Alice", "Bob", "Carol"].to_sentence

// Returns: "Alice, Bob and Carol"
arr.length === 0 ? "" :
  arr.length === 1 ? arr[0] :
  arr.slice(0, -1).join(", ") + " and " + arr[arr.length - 1]

Usage with ERB Filter

The ActiveSupport filter pairs well with the ERB filter for converting Rails templates to JavaScript:

require "ruby2js"
require "ruby2js/filter/active_support"
require "ruby2js/filter/erb"
require "ruby2js/erubi"

template = <<~ERB
<% if @user.name.present? %>
  <h1><%= @user.name.truncate(30) %></h1>
<% end %>
ERB

src = Ruby2JS::Erubi.new(template).src
puts Ruby2JS.convert(src, filters: [:erb, :active_support], eslevel: 2020)

Limitations

These methods provide simplified JavaScript equivalents. Some edge cases may behave differently from Rails:

• blank? checks for null, empty length, or empty string. It doesn’t handle other “blank” values like false or whitespace-only strings.
• to_sentence uses hardcoded “and” connector (no internationalization support)
• truncate doesn’t support :separator option for word boundaries