Ruby vs. Javascript

A guide to ruby through comparison with javascript.

Comments

In JS, we use line and multiline comments.

// here's a line comment

/* And a multiline
   comment
*/

In Ruby, multiline comments exist, but we generally use line comments with hashtags, for readability.

# here is a line comment

# here is a block
# of comments
# for you to read

Output

javascript:

console.log("hello");

ruby:

puts "hello"

Data Types

Nothingness

Just as Javascript uses undefined or null, ruby uses nil

my_bank_account = nil

Booleans

A binary representation: either true or false

is_operating = true
is_broken = false

Numbers

Datatypes used to represent a number

• Fixnum: 23
• Bignum: 23238923859348534535
• Float: 23.23

Strings

A primitive datatype used to represent a string of characters

Note that strings in ruby have many methods you can call that manipulates them in common ways. If you needed to transform a string in some way, ruby probably has a method for it.

Methods

.split
.index
.upcase
.downcase
.sub
.gsub
.capitalize

Examples

person = 'instructor'

person.split('')
#=> ["i", "n", "s", "t", "r", "u", "c", "t", "o", "r"]

person.index('tr')
#=> 3

person.upcase
#=> "INSTRUCTOR"

person.downcase
#=> "instructor"

person.sub('r', 'a')
#=> "instauctor"
# note that only the first character is replaced

person.gsub('r', 'a')
#=> "instauctoa"
# note that all character instances are replaced

person.capitalize
#=> "Instructor"

person.reverse
#=> "rotcurtsni"

person.length
#=> 10

Conditionals

Conditionals work the same way in ruby. The only difference is the end syntax and the absence of "truthy/falsy".

if
elsif
else
unless

No Falsy / Truthy

Ruby won't compare two things that are different types. You can cast them if you want to compare.

javascript:

"1" == 1 // -> true
"1" === 1 // -> false

ruby:

"1" == 1 // -> false
"1" == 1.to_s // -> true

If/Else

course = "wdi"
if course == "uxdi"
  puts "Hello, User Experience Designer!"
elsif course == "fewd"
  puts "Hello, Front-End Developer"
elsif course == "wdi"
  puts "Hello, Immersed Student"
else
  puts "Who are you?"
end

Data Structures

Arrays

An indexed arrangement of objects

several ways to create an array

arr = [1,2,3]
#=> [1,2,3]

Array Methods

Just like strings arrays have a huge list of methods that can be used to manipulate them.

.sort
.reverse
.concat
.length
.push # (<<)
.shuffle
.shift
.unshift
.slice # (negative indicies or ranges, use ! to "splice")
.first
.last
.delete
.delete_at
.inspect

Examples

numbers = [4, 2, 3, 1]

numbers.sort
# => [1, 2, 3, 4]

numbers.reverse
# => [1, 3, 2, 4]

numbers.concat([5, 6, 7])
# => [4, 2, 3, 1, 5, 6, 7]

numbers.length
# => 7

numbers.push(8)
# => [4, 2, 3, 1, 5, 6, 7, 8]

numbers << 9
# => [4, 2, 3, 1, 5, 6, 7, 8, 9]

numbers.shuffle
# => output will vary

numbers.shift
# => 4
numbers
# => [2, 3, 1, 5, 6, 7, 8, 9]

numbers.unshift(4)
# => [4, 2, 3, 1, 5, 6, 7, 8, 9]

numbers.slice(0, 2)
# => [4, 2]
numbers
# => [4, 2, 3, 1, 5, 6, 7, 8, 9]

numbers.slice!(0, 2)
# => [4, 2]
numbers
# => [3, 1, 5, 6, 7, 8, 9]

numbers.first
# => 3

numbers.last
# => 9

numbers << 'a'
# => [3, 1, 5, 6, 7, 8, 9, "a"]
numbers.delete('a')
# => "a"
numbers
# => [3, 1, 5, 6, 7, 8, 9]

numbers.delete_at(0)
# => 3
numbers
# => [1, 5, 6, 7, 8, 9]

Hashes

A javascript object is called a hash in ruby. The word "object" refers to something else.

dog = {
  :name => 'Hamlet',
  :breed => 'Pug',
  :fav_food => 'pate'
}
cat = {
  name: 'Simba',
  breed: 'American Shorthair',
  fav_food: 'Prosciutto'
}
dog[:name]
=> 'Hamlet'
cat[:fav_food]
=> 'Prosciutto'

Symbols

This is a datatype that doesn't exist in JS. Used in the place of a string, almost always as a key in a hash (object)

javascript:

my_object = {
  foo: "bar"
}

my_hash["foo"] # -> "bar"
my_hash.foo # -> "bar"

ruby:

my_hash = {
  foo: "bar"
}

my_symbol = :foo

my_hash[my_symbol] # -> "bar"
my_hash[:foo] # -> "bar"

Enumerables and Collections

Enumberables are a kind of module that you use to manipluate collections (collections are arrays and hashes)

A collection has methods that you can call on it that does the same job as a for loop: visits every value so that you can do something at each value.

Like the other plain data types, ruby gives many different kinds of iteration methods on collections- most types of repeating actions you want to do on a collection of things, ruby has it.

Each

The simplest example is each which replaces a for loop (or the JS forEach function)

.each is a module method implemented for every kind of collection (array and hash)

ark = ['cat', 'dog', 'pig', 'goat'] 
ark.each do |animal|
   puts animal
end

do end blocks

These keywords denote the beggining and end of a block. do end is specifically used to specify the block for an enumberable

def end are used to specify a function

These are a kind of replacement for curly braces.

In javascript:

for( var item in my_object ){
  console.log( item );
}

or

my_array.forEach(function(item){
  console.log( item );
});

In ruby:

my_hash.each do |item|
  puts item
end

No Callbacks

You can't set anything to happen at a later time with anonymous functions.

Functions

In Javascript

• anonymous: function (param1, [..param2, [...]]){...},
• named: function Name(param1, [..param2, [...]]){...}
• uses lexical scope
• used as values (functional programming)
• require explicit return
• all params are optional

In Ruby

• uses def
• does not capture scope
• not used as values
• implicitly returns last evaluation
• optional parameters must be specified

Examples

def say_hello
  puts "Hello, World!"
end

say_hello()

# is the same as

def say_hello
  puts "Hello, World!"
end

# note missing parentheses
say_hello

In Ruby, leaving the () off of a function call is possible. Since functions can't be passed as values (i.e., aren't first-class), Ruby knows that we mean to call the function, so it calls it.

Parameters (Arguments)

def say_hello(friend)
  puts "Hello, #{friend}!"
end

say_hello("Tim")

# is the same as
def say_hello(friend)
  puts "Hello, #{friend}!"
end

# note the lack of parentheses
say_hello "Tim"

Keyword Arguments

def say_hello(friend: 'Tim')
  puts "Hello, #{friend}!"
end

# note that there are no arguments
say_hello

Return Values

def add(num1, num2)
  return num1 + num2
end

sum = add(2, 3)
puts "2 + 3 = #{sum}"

# is the same as
def add(num1, num2)
  # note the lack of explicit return
  num1 + num2
end

sum = add(2, 3)
puts "2 + 3 = #{sum}"

Ruby will automatically return the value of the last evaluated expression. This is called having "implicit returns". You are free to have an explicit return statement, but you don't have to.

Scope

Ruby variable accessibility makes mch more sense than javascript's.

foo = 'bar' # -> bar

if true == true
  puts foo # -> bar
  foo = 'baz'
  puts foo # -> baz

end

puts foo # -> baz

banana = ['a','b','c','d','e']

banana.each do |foo|
  puts "insuide each thingy: #{foo}"
  foo = 'ggg'
  puts "insuide each: #{foo}" # (array items)
  foo = 'haha'
end

puts foo # -> baz

def monkey
  puts foo # -> error, undefined
end

puts "monkey: #{monkey}"

Tools

npm

In ruby, the functionality of npm is split into two different programs.

npm install -g

gem

This is the system to install all libraries for any ruby program.

gem is the online repository for all ruby libraries that are publicly published.

gem install is the command you run to install a library.

gem does not create a directory like node_modules. Your library files are stored in a central place on your computer.

By default, when you install a gem, that code is available anywhere on your computer, like npm install -g.

Gemfile

Gemfile is the package.json of ruby.

bundler

npm init

bundle init

Installing those libraries on your system runs through a different command, one just for projects using a Gemfile.

npm install

bundle install

get one library

npm install express

bundle add rails

Pairing Exercise

(ruby for begginers)