Syntax differences between Ruby and Javascript

I’ve been working with Javascript for a while now, and have gotten fairly comfortable with its syntax.

I’m now also using Ruby again, which has a slightly different flavor.

Here are some of the main syntactical differences between the two languages, in table format.

1. Basics

	Javascript	Ruby
Naming convention for variables, functions, and methods	camelCase	snake_case
Naming convention for classes	PascalCase	PascalCase
Declaring variables	let someArray = [1,2]; Although var was exclusively used in older codebases, let is now more encouraged because let is block scoped while var is function scoped and can cause unintended consequences	some_array = [1,2]
Declaring constants	const SOMECONSTANT = 3.14; Reassigning something else to the constant will throw an error	SOME_CONSTANT = 3.14 Ruby will throw a warning when attempting to reassign something else to the constant, but will let you do it
Declaring global variables	Declare the variable with let or const in the global context. However, if a variable with the same name is declared in a local scope, the local variable will be usable in that scope but not the global variable	You can declare a global variable anywhere by using a $ just in front of the variable name (e.g. $this_is_a_global_variable = 2100 )
Comments	//this is a single-line comment in JS /* This is a multi-line comment in JS */	#this is a single-line comment in Ruby =begin This is a multi-line comment in Ruby =end
Print to console (automatically adding new line)	console.log(‘hello world’);	puts ‘hello world’
Print to console (without new line)	process.stdout.write(‘hello’);	print ‘hello’
Conditional Statements	if (someCondition) {   //do this   //and this } else if (someOtherCondition) {   //do this instead } else {   //otherwise do this }	if some_condition   #do this   #and this elsif some_other_condition   #do this instead else   #otherwise do this end
one-line conditional statement	if (condition) doThis;	do_this if condition
Ternary conditional expression	condition ? doThisIfTrue : doThisIfFalse;	condition ? do_this_if_true : do_this_if_false
Switch / case statement	switch(expression) {    case x:      // code block      break;    case y:      // code block      break;   default:      // code block } If you do not break, JS will execute every line after that case too	case expression    when x     #code block    when y     #code block    else     #code block end
Define a function / method	function someFunction(param1, param2){   //do stuff   return something; } If the return keyword is never used, the function will return undefined	def some_method(param1, param2)   #do stuff   return something end If the return keyword is never used, the method will return whatever is calculated on the last line before the end statement.
Keyword to refer to the current particular instantiated object	this	self
Error handling	try {   // do something risky } catch(err) {   // handle error here }	begin    # do something risky rescue   # handle error here end

2. Arrays & Strings

	Javascript	Ruby
Map / Collect method (Returning a new array of tweaked elements from an original array)	const newArray = someArray.map(el => el * 2)	new_array = some_array`.map {	el	el * 2}<br><br> * To mutate the *original* array, usemap!instead ofmap<br> * Thecollectmethod is the same asmap`
Iterate through an array’s elements in one line and no need for index #	someArray.forEach( el => console.log(el));	some_array`.each {	el	puts el}`
Iterate through an array’s elements to perform a block requiring index #	for(let i=0; i < someArr.length; i++){   console.log(i, someArr[i]);   // rest of block }	some_arr`.each_index do	i	<br> &nbsp;&nbsp; puts i, some_arr[i]<br> &nbsp;&nbsp;# rest of block <br>end<br><center>-- or --</center><br> (0..some_arr.length-1).each do	i	<br> &nbsp;&nbsp;puts i, some_arr[i]<br> &nbsp;&nbsp;# rest of block <br>end`
Delete an element at index i of an array	someArray.splice(i,length); Where i=index # to start deleting, and length = # of elements to delete	some_array.delete_at(i) To delete all elements of a particular value (e.g. ‘cat’) regardless of index number, use: some_array.delete(‘cat’)
Return the unique values of an array	const uniqueArray = [...new Set(someArray)];	unique_array = some_array.uniq To mutate the original array and retain only its unique values, use: someArray.uniq!
Filter an array	const filteredArray = someArray.filter(el => el > 5); E.g. Returns all elements in someArray greater than 5	filtered_array = some_array`.select {	el	el > 5}` E.g. Returns all elements in some_array greater than 5
Check if an element is in an array	someArray.includes(5); E.g. Returns true if someArray has an element with a value of 5	some_array.include?(5) E.g. Returns true if some_array has an element with a value of 5 For methods that return a boolean, a Ruby convention is to name them with a ? at the end
Sorting an array in Ascending order	someArray.sort((a,b)=>a-b) This mutates the original array	some_arr.sort This does not mutate the original array. To do that, use .sort! instead
Sorting an array in Descending order	someArray.sort((a,b)=>b-a) This mutates the original array	some_arr`.sort {	a, b	b <=> a } <br><br>This does not mutate the original array. To do that, use.sort!` instead
Template Literals / String Interpolation	console.log(` Welcome onboard, ${someName}`); The use of backticks are required for template literals.	puts ` Welcome onboard, #{some_name}` You can use backticks, or double quotes (but not single quotes)
String Concatenation	someString = ‘Hi,’ + someName; If the left side of the + is a string, then JS will coerce anything that appears on the right side into a string too, even if it’s a number or another data type	some_string = ‘Hi,’ + some_name Ruby will throw an error if you attempt to concatenate a string with a non-string. You must convert it to a string first (i.e. .to_s)
Convert a number to a string	let varString = someNum.toString();	var_string = some_num.to_s
Convert a string to an integer	let varNum = Number(someString);	var_num = some_string.to_i
Convert a string to a float	let varNum = parseFloat(someString);	var_num = some_string.to_f

3. Objects / Hashes

	Javascript	Ruby
Key-value pair data type is called	an object	a hash
object/hash creation + assignment (Literal notation)	const someObject = {key1: value1, key2: value2};	the older, symbol & hash-rocket method: some_hash = {:key1 => value1, :key2 => value2} or the newer, cleaner method: some_hash = {key1: value1, key2: value2}
Object/hash creation (class instantiation notation)	const someObject = new Object;	some_hash = Hash.new
Add key/value pair to an existing object/hash	someExistingObject[key3] = value3; or someExistingObject.key3 = value3;	some_existing_object[:key3] = value3
Iterate through an object/hash in one line	for(let key in someObject) { console.log(key,someObject[key])};	some_hash`.each {	key,value	puts key,value}<br><br> Using the.eachmethod on a hash with only one parameter (e.g.	el	) would make that variable an array of two elements: the key at 0 (el[0]), and the value at 1 (el[1]`)
convert an object/hash to an array of sub-arrays of [key,value]	const someArray = Object.entries(someObject);	some_array = some_hash.to_a
Delete a key/value pair	delete someObject[someKey];	some_hash.delete(some_key)
Check if an object/hash has a key	someObject.hasOwnProperty(someKey)	some_hash.has_key?(some_key) - or - the fetch method allows you to get the value at the key or specify an alternative return value if the key doesn’t exist: some_hash.fetch(some_key, “error message”)