This document compares quirks between Ruby and JavaScript by providing examples of code snippets and their outputs in each language. Some key differences highlighted include: - Variable and method definitions behave differently, with Ruby raising errors and JavaScript returning undefined. - String concatenation and addition rules are not the same, such as adding objects to strings. - NaN and null/undefined behaviors like type coercion and method calls have inconsistencies. - Boolean logic and comparisons like == have unexpected outcomes in JavaScript. - Syntax errors occur in different cases, such as extra braces in Ruby. - Object comparisons and primitive wrapping give different results between the languages.

1. Ruby & Javascript
Quirks
Suman Mukherjee

2. Inspiration for the talk
Gary Bernhardt’s talk @ CodeMash 2012
https://www.destroyallsoftware.com/talks/wat

3. Ruby Javascript
> var_1 = var_2 > var1 = var2
# NameError: undefined local variable # ReferenceError: var2 is not defined
or method var2
> var1
> var_1 ReferenceError: var1 is not defined
# nil

4. Ruby Javascript
> “John” + {} > “John” + {}
# TypeError: can't convert Hash into # 'John[object Object]'
String

5. Ruby Javascript
> var_3 = var_3 > var3 = var3
# ReferenceError: var3 is not defined
# nil

6. Ruby Javascript
> [1, 2] + [3, 4] > [1, 2] + [3, 4]
# '1,23,4'
# [1, 2, 3, 4]

7. Ruby Javascript
> {} + [] Node
# NoMethodError: undefined method `
+' for {}:Hash
> {} + []
# '[object Object]'
Chrome console
> {} + []
#0

8. Ruby Javascript
> [] + {} > [] + {}
# TypeError: can't convert Hash into # '[object Object]'
Array

9. Ruby Javascript
> [] + [] > [] + []
# ‘’
# []

10. Ruby Javascript
> {} + {} Node
# NoMethodError: undefined method `
+' for {}:Hash
> {} + {}
# '[object Object][object Object]'
Chrome console
> {} + {}
# NaN

11. Ruby Javascript
> “blah” + 3 > “blah” + 3
# TypeError: can't convert Fixnum into # “blah3”
String

12. Ruby Javascript
> “blah” - 3 > “blah” - 3
# NoMethodError: undefined method # NaN
`-' for "blah":String

13. Ruby Javascript
> “blah” * 3 > “blah” * 3
# NaN
# "blahblahblah"

14. Javascript
Ruby
> parseInt(undefined)
> nil.to_i # NaN
#0 > parseInt(null)
# NaN
> “”.to_i > parseInt(“”)
#0 # NaN
> undefined.toString()
# TypeError: Cannot call method
> nil.to_s 'toString' of undefined
# “”
> null.toString()
# TypeError: Cannot call method
> 10.to_s 'toString' of null
# “10” > 10.toString()
# SyntaxError
> (10).toString()
# ’10’

15. Ruby Javascript
> 0/0 > 0/0
# ZeroDivisionError: divided by 0 # NaN
> 0.0/0 > 0.0/0
# NaN # NaN

16. Ruby Javascript
> “NaN”.to_f > parseFloat(“NaN”)
# 0.0 # NaN

17. Ruby Javascript
> “” == false > “” == false
# true
# false
> [] == false > [] == false
# true
# false
> 0 == false > 0 == false
# true
# false

18. Ruby Javascript
> 0 && [] > 0 && []
# [] #0
> [] && 0 > [] && 0
#0 #0
> 0 && “” > 0 && “”
# “” #0
> “” && 0 > “” && 0
#0 # “”
> [] && “” > [] && “”
# “” # “”
> “” && [] > “” && []
# [] # “”

19. Ruby Javascript
> 5 == ‘5’ > 5 == ‘5’
# true
# false

20. Ruby Javascript
> {“grrrhhh”} > {“grrrhhh”}
# 'grrrhhh'
# SyntaxError: compile error

21. Ruby Javascript
> “a”===String.new(“a”) > “a”===new String(“a”)
# false
# true

22. Thank You
Follow me @mukherjeesuman