What does += %w mean in the line used to precompile assets in assets.rb?

Question

I'm looking at the default file placed in /config/initializers/assets.rb in a Rails 5 app.

To precompile code, Rails inside the comments, gives a pre-existing code to precompile assets together.

Rails.application.config.assets.precompile += %w( search.js )

I am curious what the last part means: += %w( search.js ), as I have never seen the expression (+= %w) used in Ruby or Rails. I know that the entire line is calling the Rails class, chaining some methods together to create the end output. But I am curious, what does the += %w do, and how is it affecting what I presume to be the argument (search.js)?

`%w` is shorthand for an array of strings, in your case `[ 'search.js' ]` — Jared, Jan 06 '17 at 20:16

Eyeslandic · Accepted Answer · 2017-01-06T20:17:25.077

3

Rails.application.config.assets.precompile += %w( search.js )

is equal to doing

Rails.application.config.assets.precompile = Rails.application.config.assets.precompile + ['search.js']

To break it down, += is just the regular operator for including the lefthand side in the statement. Like

i = 0
i += 1 # i = i + 1

%w enables you to create an array like this

%w(search.js profile.js error.js)

which is just a nice shorthand for

['search.js', 'profile.js', 'error.js']

edited Jan 06 '17 at 20:17

answered Jan 06 '17 at 20:14

Eyeslandic

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So is Rails.application.config.assets.precompile an array, and you're simply adding to that array via the += %w? – the12 Jan 06 '17 at 20:25
3

@the12 That's correct. – Wayne Conrad Jan 06 '17 at 20:41

What does += %w mean in the line used to precompile assets in assets.rb?

1 Answers1