View helpers in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this Rails view helper output?

Given the helper method below, what will be the rendered HTML output when called in a view?

module ApplicationHelper
  def greeting(name)
    content_tag(:p, "Hello, #{name}!")
  end
end

# Called in view as: <%= greeting('Alice') %>

Ruby on Rails

module ApplicationHelper
  def greeting(name)
    content_tag(:p, "Hello, #{name}!")
  end
end

A <p>greeting('Alice')</p>

B Hello, Alice!

C <div>Hello, Alice!</div>

D <p>Hello, Alice!</p>

💡 Hint

Remember that content_tag creates an HTML tag with content inside.

The content_tag helper wraps the string inside the specified HTML tag, here a paragraph

. So the output is a paragraph with the greeting text.

📝 Syntax

intermediate

Which option correctly defines a Rails helper method to format a date?

You want to create a helper method that formats a Date object as 'Month day, Year' (e.g., 'April 5, 2024'). Which of the following method definitions is correct?

A

def format_date(date)
  date.strftime('%B %d, %Y')
end

B

def format_date(date)
  date.to_s('%B %d, %Y')
end

C

def format_date(date)
  date.format('%B %d, %Y')
end

D

def format_date(date)
  date.strftime('%b %d %Y')
end

💡 Hint

Check the Ruby Date class methods for formatting dates.

The strftime method formats dates with the given pattern. '%B' is full month name, '%d' is day with leading zero, '%Y' is four-digit year.

🔧 Debug

advanced

Why does this helper method cause an error?

Consider this helper method:

def link_to_profile(user)
  link_to "Profile", user_path(user.id)
end

When called with link_to_profile(nil), it raises an error. Why?

Ruby on Rails

def link_to_profile(user)
  link_to "Profile", user_path(user.id)
end

A Because user_path cannot accept an integer argument

B Because user is nil, calling user.id raises NoMethodError

C Because link_to requires a block when user is nil

D Because the method link_to_profile is missing a return statement

💡 Hint

What happens if you call a method on nil in Ruby?

Calling user.id when user is nil causes NoMethodError since nil has no id method.

❓ state_output

advanced

What is the output of this helper with conditional logic?

Given this helper method:

def status_badge(active)
  if active
    content_tag(:span, "Active", class: "badge badge-success")
  else
    content_tag(:span, "Inactive", class: "badge badge-danger")
  end
end

# Called in view as: <%= status_badge(false) %>

Ruby on Rails

def status_badge(active)
  if active
    content_tag(:span, "Active", class: "badge badge-success")
  else
    content_tag(:span, "Inactive", class: "badge badge-danger")
  end
end

A <span class="badge badge-danger">Inactive</span>

B <span class="badge badge-success">Active</span>

C <span>Inactive</span>

D Active

💡 Hint

Check the condition and which content_tag is returned.

When active is false, the else branch runs, producing a span with class 'badge badge-danger' and text 'Inactive'.

🧠 Conceptual

expert

Which statement about Rails view helpers is true?

Choose the correct statement about Rails view helpers:

A Helpers can only be used in views and never in controllers or models

B Helpers are automatically available in views but must be explicitly included in controllers

C Helpers can be used to keep view templates clean by moving complex logic out of them

D Helpers must always return raw HTML strings without escaping

💡 Hint

Think about the purpose of helpers in MVC architecture.

Helpers are designed to keep views simple by moving formatting and presentation logic out of templates.

Practice

1. What is the main purpose of view helpers in Rails?

easy

A. To handle database queries and data storage

B. To generate HTML or text for views in a clean and reusable way

C. To manage user sessions and authentication

D. To configure routes and URL patterns

Solution

1. Step 1: Understand the role of view helpers

   View helpers are Ruby methods designed to create HTML or text snippets for views, making the code cleaner and reusable.

2. Step 2: Differentiate from other Rails components

   Helpers do not handle database, sessions, or routing; those are handled by models, controllers, and routes respectively.

3. Final Answer:

   To generate HTML or text for views in a clean and reusable way -> Option B

4. Quick Check:

   View helpers = generate HTML/text [OK]

Hint: Helpers create HTML/text for views, not data or routes [OK]

Common Mistakes:

• Confusing helpers with models or controllers
• Thinking helpers manage database or sessions
• Assuming helpers configure routes

2. Which of the following is the correct way to use a Rails view helper in an ERB template?

easy

A. <%= link_to 'Home', root_path %>

B. <% link_to 'Home', root_path %>

C. <%= link_to 'Home', 'root_path' %>

D. <%== link_to 'Home', root_path %>

Solution

1. Step 1: Identify correct ERB syntax for output

   To display the result of a helper method, use <%= ... %> which outputs the returned HTML.

2. Step 2: Check the helper usage

   link_to 'Home', root_path correctly calls the helper with a path helper method, not a string.

3. Final Answer:

   <%= link_to 'Home', root_path %> -> Option A

4. Quick Check:

   Use <%= ... %> to output helper results [OK]

Hint: Use <%= ... %> to output helper results in ERB [OK]

Common Mistakes:

• Using <% ... %> which does not output content
• Passing path as a string instead of method
• Using <%== ... %> which is for raw HTML, not needed here

3. Given this helper method in app/helpers/application_helper.rb:

def greeting(name)
  "Hello, #{name}!"
end

What will this ERB code output?

<%= greeting('Alice') %>

medium

A. Hello, Alice!

B. greeting('Alice')

C. Hello, name!

D. Error: undefined method 'greeting'

Solution

1. Step 1: Understand the helper method behavior

   The method greeting takes a name and returns the string "Hello, #{name}!" with the name inserted.

2. Step 2: Evaluate the ERB output

   The ERB tag <%= greeting('Alice') %> calls the method with 'Alice' and outputs the returned string.

3. Final Answer:

   Hello, Alice! -> Option A

4. Quick Check:

   Helper returns string with name inserted [OK]

Hint: Helpers return strings; <%= ... %> outputs them [OK]

Common Mistakes:

• Thinking it outputs the method call as text
• Confusing variable interpolation syntax
• Assuming helper is undefined if not included

4. You wrote this helper method:

def format_price(price)
  "$#{price.round(2)}"
end

But in your view, calling <%= format_price(5) %> shows an error: NoMethodError: undefined method 'round' for 5:Integer. What is the problem?

medium

A. You must call round with parentheses: round(2)

B. Helpers cannot use Ruby methods like round

C. The dollar sign should be escaped as \$

D. Integer does not have a round method; convert to float first

Solution

1. Step 1: Understand the error message

   The error says Integer (5) has no method 'round', which is true because round is a Float method.

2. Step 2: Fix the method to convert price to float

   Convert price to float before calling round, e.g., price.to_f.round(2), so rounding works.

3. Final Answer:

   Integer does not have a round method; convert to float first -> Option D

4. Quick Check:

   round works on floats, not integers [OK]

Hint: Use to_f before round to avoid Integer errors [OK]

Common Mistakes:

• Assuming round works on integers
• Thinking parentheses cause the error
• Believing helpers can't use Ruby methods

5. You want to create a helper that generates a list of user names as an unordered HTML list. Which helper method implementation correctly returns safe HTML for this in Rails?

hard

A. def user_list(users)
users.each { |u| "#{u.name}" }
end

B. def user_list(users)
"" + users.map { |u| "#{u.name}" }.join + ""
end

C. def user_list(users)
content_tag(:ul) do
users.map { |u| content_tag(:li, u.name) }.join.html_safe
end
end

D. def user_list(users)
content_tag(:ul, users.map { |u| content_tag(:li, u.name) })
end

Solution

1. Step 1: Understand safe HTML generation in helpers

   content_tag with a block correctly wraps the list items in <ul> tags, and joining with html_safe marks the string safe.

2. Step 2: Analyze each option

   def user_list(users) content_tag(:ul) do users.map { |u| content_tag(:li, u.name) }.join.html_safe end end uses content_tag with block and html_safe join, which is correct. def user_list(users) "
   " + users.map { |u| "
   • #{u.name}
   " }.join + "
   " end returns a string but lacks html_safe, risking unsafe output. def user_list(users) users.each { |u| "
3. #{u.name}
" } end returns an array, not a string. def user_list(users) content_tag(:ul, users.map { |u| content_tag(:li, u.name) }) end passes an array as content_tag content, which renders incorrectly.

4. Final Answer:

   def user_list(users) content_tag(:ul) do users.map { |u| content_tag(:li, u.name) }.join.html_safe end end -> Option C

5. Quick Check:

   Use content_tag with block and html_safe join [OK]

Hint: Use content_tag with block and join(...).html_safe for lists [OK]

Common Mistakes:

• Returning raw strings without html_safe
• Passing arrays directly to content_tag content
• Using each instead of map for generating list items