CSS: Matching against attributes and their values (or parts of them)
You probably know that you can use CSS selectors to match against elements and their attributes, such as:
a[title] { /* any <a> that has a "title" */ }
a[data-fancy="true"] { /* any <a> that has their "data-fancy" attribute set to "true" */ }
But there is more: You do not need to match against "full" attribute values but can match against parts of them.
They work in all somewhat modern browsers, and IE9 or later.
- Exact match (CSS2)
-
[foo="bar"](matches<div foo="bar" />, but not `<div…
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 monkey-patch:
```
class ActionView::Helpers::FormBuilder
def flat_grouped_collection_select(fi…
8 steps for fixing other people's code
Guide how to make fixes in other people's GitHub repositories. It's basically "Open Source Development 101".
Way back in mid-2007, when Rails 1.2 was the new hotness and GitHub was still a year away from crawling out of the primordial internet soup, prolific open source contributor Dr Nic wrote an article titled “8 steps for fixing other people’s code”. (…)
Here in the fantastical future world of 2012, while we still don’t have hoverboards or household nuclear fusion, we do have some great tools that make fixing other people’s code…
Do not pass an empty array to ActiveRecord.where when using NOT IN
Be careful with the Active Record where method. When you accidentally pass an empty array to the where method using NOT IN, you probably will not get what you expected:
User.where("id NOT IN (?)", [])
=> SELECT `users`.* FROM `users` WHERE (id NOT IN (NULL))
Even though you might expect this to return all records, this actually results none.
Never use the expression id NOT IN (?) in any scope! See below some workarounds.
Rails < 4
Rails < 4 does not provide a pretty workaround.
```
ids = []
if ids.present?
Us…
AngularJS 1 Performance: One-time bindings in expressions
In addition to the {{ myValue }} two-way binding syntax, since Angular 1.3 there's a one-time binding syntax, prefixing the value or expression with ::, e.g. {{ ::myValue }}, {{ ::myValue >= 42 }} and {{ ::myExpression(value) | someFilter }}.
One-time bound expressions get dropped from the list of watchers as soon as they can be resolved. Performance-wise the impact for this small change is huge, since Angular apparently slowes down with too many watchers registered [(Source)](http://www.binpress.com/tutorial/speeding-up-angular-js-wi…
How to create memory leaks in jQuery
jQuery doesn't store information about event listeners and data values with the element itself. This information is instead stored in the global $.cache object. Every time you add an event listener or data value to a jQuery object, $.cache gains another entry.
The only way that a $.cache entry gets deleted is when you call remove() on the element that put it there!
Since cache entries also have a pointer back to the element that spawned them, it is easy to create DOM elements that can never be garbage-collected.
Below are …
Ruby: required keyword arguments in the pre-2.1 era
Starting with Ruby 2.0 you can define methods with keyword arguments.
In 2.1+ required keyword arguments can be defined by using a colon without default value:
def match(value, ignore:)
...
end
To accomplish something similar in ruby 1.8, use:
def match(value, options = {})
ignore = options.fetch(:ignore)
...
end
How to examine an unknown Ruby object
When debugging your application, you will come across objects created by some gem or framework. You don't have the source code at hand, still need to inspect this object. Here are some tools to do so:
Relevant methods
@object.methods - Object.instance_methods returns a list of methods excluding methods inherited from Object. This makes the methods list drastically more relevant. You can also try subtracting other base classes like ActiveRecord::Base.methods etc.
Filtering method list
@object.methods.grep /keyword/ comes…
Ruby tempfiles
Tempfiles get deleted automatically
With the the ruby Tempfile class you can create temporary files. Those files only stick around as long as you have a reference to those. If no more variable points to them, the GC may finalize the object at some point and the file will be removed from the filesystem. If you would try to access your tempfile then using its path (which you stored previously), you would get an error because the file no longer exists.
Unlink your tempfiles when you're done with them
-…
Defining class methods with Modularity traits
There are two ways to define a class method from a Modularity trait. Note that the usual caveats regarding class method visibility apply.
Using define_method
The recommended way is to define a method on your module's singleton class:
# ruby 1.9+
module SomeTrait
as_trait do
define_singleton_method :foo do
# ...
end
...
Javascript: Comparing two arrays for equality
Don't Google this, you will lose all will to live. Instead use Object#isEqual from Lodash or Underscore.js:
_.isEqual([1, 2], [2, 3]) // => false
To compare two arrays for equality in a Jasmine spec assertion, see Jasmine: Testing complex types for equality.