Javascript: Don't throw exceptions from async functions

TLDR: A function is hard to use when it sometimes returns a promise and sometimes throws an exception. When writing an async function, prefer to signal failure by returning a rejected promise.

The full story

When your function returns a promise ("async function"), try not throw synchronous exceptions when encountering fatal errors.

So avoid this:

function foo(x) {
if (!x) {
throw "No x given"
} else
return new Promise(function…

Auto-destruct in 18 days

Unpoly 0.32.0 released


Compatible changes

  • Fix a bug where morphing an [up-keep] element with a destructor would throw an error.
  • Fix a bug where an [up-keep] element would lose its jQuery event handlers when it was kept.
  • Fix a bug where up.log.disable() did not persist through page reloads.
  • Fix a bug where up.reveal would scroll too far if the viewport has a padding-top.
  • Fix a bug where [up.reveal](ht…

Use Memoizer instead of ActiveSupport::Memoizable

ActiveSupport::Memoizable will be removed from Rails and has a lot of strange caveats that will ruin your day.

Use the Memoizer gem instead. It works in all past and future Railses and has none of the annoying "features" of ActiveSupport::Memoizable. It just does memoization and does it well.

The syntax is similiar also:

class Foo
include M…


It's OK to put block elements inside an <a> tag

In general, you should not put a block element inside an inline element. So don't do this:


The browser will think you wrote invalid HTML by accident, and will sometimes reorder elements silently.

There is one notable exception: It's OK to wrap block elements in a <a> tag in HTML5 (not 4). The spec days:

The a element may be wrapped around entire paragraphs, lists, tables, and so forth, even entire sections, so long …

Search everywhere in RubyMine

Have you tried the Search everywhere dialog? You can open it by pressing Shift twice.



A non-weird replacement for grouped_collection_select

Rails comes with grouped_collection_select that appears to be useful, but isn't.

As an alternative, consider the flat_grouped_collection_select found below. It takes a third argument that extracts the group from each element in the collection:

= form.flat_grouped_collection_select :user_id, users, :department, :id, :full_name

Here is the code:

def flat_grouped_collection_select(field, collection, group_label_method, value_method,…

External content

An Introduction to Sending HTML Email for Web Developers

A comprehensive introduction to sending HTML emails.


HTML email: Two words that, when combined, brings tears to a developer’s eyes. If you’re a web developer, it’s inevitable that coding an email will be a task that gets dropped in your lap at some time in your career, whether you like it or not. Coding HTML email is old school. Think back to 1999, when we called ourselves “webmasters” and used Frontpage, WYSIWYG editors and tables to mark up our websites.

Table of Contents

  • Introduction To Sending Email Link
  • Email List B…

How to iterate over an Enumerable, returning the first truthy result of a block ("map-find")

Ruby has Enumerable.find(&block), which returns the first item in the collection for which the block evaluates to true.

first_post_with_image = posts.find do |post|

However, sometimes it's not the item you're interested in, but some value depening on it – e.g. the value the block evaluated to. You could first map the collection and then take the first truthy value, but this way you need to process the whole collection twice:

first_image_url =

If the mapping …

Puppet: Could not evaluate: Field 'device' is required

If you get an error like this for a puppet mount:

$ > puppet agent –test
Info: Retrieving pluginfacts
Info: Retrieving plugin
Info: Loading facts
Info: Caching catalog for
Info: Applying configuration version '1483001792'
Info: Computing checksum on file /etc/fstab
Info: FileBucket got a duplicate file {md5}34b9adc036cf1dbd2392df84f921547d
Notice: /Stage[main]/Foobar/Swap_file::Files[default]/Mount[/var/swapfile]/ensure: defined 'ensure' as 'defined'
Error: /Stage[main]/Foobar/Swap_file::Files[default]/Mount[/var/s…


Live CSS / view reloading

Next time you have to do more than trivial CSS changes on a project, you probably want to have live CSS reloading, so every time you safe your css, the browser updates automatically. It's pretty easy to set up and will safe you a lot of time in the long run. It will also instantly reload changes to your html views.

Simply follow the instructions below, taken from

Install CSS live reload (only once per project)

  1. Add th…

How to doubleclick in Selenium

Put the attached file into features/support/.

Example usage:

When /^I open the task named "(.+?)"$/ do |task_name|
  task = page.all('.task').detect do |t|
    t.find('.label').text.downcase == task_name.downcase

Note: only Selenium understands doubleclicks.\ Credits: the attached Capybara issue discussion.

Enabling ** in your bash

You may know the double asterisk operator from Ruby snippets like Dir['spec/**/*_spec.rb'] where it expands to an arbitrary number of directories.
However, it is disabled by default on most systems. Here is how to enable it.

If you check your globstar shell option, it is probably disabled:

$ shopt globstar
globstar           off

In that case, ** behaves just like * and will match exactly 1 directory level.

$ ls spec/**/*_spec.rb

To enable it, run

shopt -s globstar

and re-open (o…

External content


Create beautiful Javascript charts with one line of Ruby.

Promising chart library for easily rendering charts with Google Charts.

This seems to not submit your data points to Google.

Ruby: String representations of regular expressions

Ruby's regular expressions can be represented differently.
When serializing them, you probably want to use inspect instead of to_s.

For the examples below, consider the following Regexp object.

regexp = /^f(o+)!/mi


Using to_s will use a format that is correct but often hard to read.

>> regexp.to_s
=> "(?mi-x:^f(o+)!)"


As the Ruby docs say:


MySQL: Creating many records works faster in a transaction

When you need to insert many records into the same table, a fast way to do it is to have a single INSERT statement describing multiple rows. Unfortunately there is no way to do this through ActiveRecord.

What you can do to save time is to open a transaction and save multiple records within that transaction:

transaction do
  500.times { Model.create! }

Although you will still trigger 500 INSERT statements, they will complete considerably faster.

When I trie…

External content

Font Combiner

Font Combiner offers a way to tweak and adjust any TTF or OTF font (license permitting), by bringing in font glyphs as vector shapes, providing a completely overhauled font generated to the user's specification with alternative metrics options, alternative hinting types, kerning and spacing options and the facility to make any average free font look great.

Examples are here

Fix Rubygems binary error: undefined method `activate_bin_path' for Gem:Module (NoMethodError)

So you're getting an error like this:

undefined method `activate_bin_path' for Gem:Module (NoMethodError)

Here is what happened:

  • You installed a recent version of Rubygems
  • You installed some gems that install a binary (like bundle, rake or rails) with code that only works with modern Rubygems versions
  • You downgraded Rubygems to an older versions, which doesn't change any binaries
  • When calling binaries with the old Rubygems version, it cannot process the line Gem.activate_pin_path(...) that was written out by th…
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