JSON library basics in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using JSON?

Consider this Ruby code that uses the JSON library to parse a JSON string. What will be printed?

Ruby

require 'json'
json_str = '{"name":"Alice","age":30}'
obj = JSON.parse(json_str)
puts obj["name"]

A SyntaxError

B 30

C nil

D Alice

💡 Hint

Think about what JSON.parse returns and how to access values in the resulting object.

JSON.parse converts the JSON string into a Ruby hash. Accessing obj["name"] returns the string "Alice".

❓ Predict Output

intermediate

What does this Ruby code output when generating JSON?

This Ruby code creates a hash and converts it to a JSON string. What is the output?

Ruby

require 'json'
hash = {"city" => "Paris", "country" => "France"}
puts JSON.generate(hash)

A {"city":"Paris","country":"France"}

B {city: "Paris", country: "France"}

C {"city":Paris,"country":France}

D SyntaxError

💡 Hint

Remember JSON keys and string values must be in double quotes.

JSON.generate converts the Ruby hash into a JSON string with keys and string values quoted properly.

🔧 Debug

advanced

What error does this Ruby code raise when parsing JSON?

Look at this Ruby code snippet. What error will it raise when run?

Ruby

require 'json'
json_str = '{name: "Bob", age: 25}'
obj = JSON.parse(json_str)

A NoMethodError

B JSON::ParserError

C TypeError

D SyntaxError

💡 Hint

Check if the JSON string is valid JSON format.

The JSON string uses unquoted keys, which is invalid JSON. JSON.parse raises JSON::ParserError.

🧠 Conceptual

advanced

Which Ruby method converts a Ruby object to a JSON string?

Which method from the JSON library converts a Ruby object like a hash or array into a JSON formatted string?

A JSON.generate

B JSON.load

C JSON.parse

D JSON.read

💡 Hint

Think about the method that creates JSON text from Ruby objects.

JSON.generate takes a Ruby object and returns a JSON string representation.

🚀 Application

expert

How many keys are in the Ruby hash after parsing this JSON string?

Given this Ruby code, how many keys does the resulting hash have?

Ruby

require 'json'
json_str = '{"a":1,"b":2,"c":{"d":4}}'
obj = JSON.parse(json_str)
puts obj.keys.size

A 1

B 4

C 3

D 2

💡 Hint

Count only the top-level keys in the parsed hash.

The JSON string has three top-level keys: "a", "b", and "c". The nested keys inside "c" do not count at the top level.