Optimize redundant array operations and string manipulations

[Copilot]

Identified and eliminated performance bottlenecks from redundant calculations, inefficient array operations, and excessive string manipulations.

JavaScript

• book_controller.js: Cache percentage getter (was invoked 3x per bookmark render); replace findIndex callback with indexOf
• index.js: Merge two regex replacements into single pass

Ruby

• books.rb:
  • Replace chained split() calls with single regex extraction (4 instances)
  • Use partition vs find + reject to avoid double iteration
  • Replace split + array subtraction with scan for word counting
  • Use ERB::Util.html_escape over manual gsub
• date_tags.rb: Cache Date.today (3 system calls → 1)

Before:

def slug
  id.split("/").last.split(".md").first
end

def calculate_word_count
  words_array = resource.content.split - %w[ # ]
  @word_count = words_array.size
end

After:

def slug
  id[/\/([^\/]+)\.md$/, 1]
end

def calculate_word_count
  @word_count = resource.content.scan(/\b(?!#\b)\w+/).size
end

Original prompt

Identify and suggest improvements to slow or inefficient code

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