JavaScript is wild and dangerous. I’ve been using it for years and time to time faced with the same issues. Also being an interviewer I talked to lots of people. And most of them able to answer the questions correctly, but can not explain why it works so. In my talk, I prepared examples of ‘what is wrong with JS’ and explained why it works so based on ECMA specifications.

1. JavaScript was
invented in
Odessa
Dmitriy
Gusev
Summer. Sea. JavaScript.

2. Who am I?

3. Welcome to Odessa

7. Type coercion was invented in Odessa

8. null and undefined

9. null and undefined

10. null and undefined

11. null and undefined

14. Unpredictable null

15. Unpredictable null

16. Unpredictable null

17. Unpredictable null

18. Unpredictable null

19. Unpredictable null

20. Unpredictable null

21. Unpredictable null

22. Unpredictable null

24. Incomparable undefined

25. Incomparable undefined

26. Incomparable undefined

27. Incomparable undefined

28. Incomparable undefined

29. Incomparable undefined

30. Incomparable undefined

31. Incomparable undefined

32. Incomparable undefined

33. Incomparable undefined

34. What the NaN?

35. What the NaN?

36. What the NaN?

37. What the NaN?

38. What the NaN?

39. What the NaN?

41. subtraction was invented in Odessa

42. subtraction

43. subtraction

44. subtraction

45. subtraction

46. subtraction

47. subtraction

48. subtraction

49. subtraction

50. subtraction

51. subtraction

52. subtraction

54. Symbol comparison was invented in
multinational Odessa

55. You don’t know about letters

56. You don’t know about letters

57. You don’t know about letters

58. You don’t know about letters

60. So ambiguous string was invented in
Odessa

61. Objects!?

62. Objects...

63. Objects...

64. Objects...

65. Objects...

66. Objects...

67. Objects...

70. Numbers were invented at Privoz, Odessa

71. Numbers

72. Iasdasdad

73. Numbers

74. Numbers

75. Numbers

77. More Numbers

78. Numbers

79. Numbers

80. Numbers

81. Numbers

82. Numbers

83. Numbers

85. parseInt()
was invented at Privoz, Odessa

86. parseInt

87. parseInt

88. parseInt - old standart ( < ES5 )

89. parseInt - happy future has come (ES5)

90. parseInt - happy future has come(ES5)

91. parseInt - happy future has come(ES5)

93. return was invented in Odessa

94. return

95. return

96. return

97. return

98. return

99. return

101. RegExp was invented in Odessa,
Minibus / Marshrutka

102. RegExp

103. RegExp

104. RegExp

105. RegExp

106. RegExp

107. Unicode was invented in Odessa

108. Unicode

109. Unicode

110. Unicode

111. Unicode

112. Unicode

113. Unicode

114. Unicode

115. Logical operators were invented
anywhere but in Odessa

116. Logical operators

117. Logical operators

118. Logical operators

119. Logical operators

120. Logical operators

121. Logical operators

122. A little bit more...

123. Operators

124. Operators

125. Logical operators

126. Logical operators

127. 2020, stop it

128. 2020, stop it

129. 2020, stop it

130. 2020, stop it

131. 2020, stop it

132. 2020, stop it

133. 2020, stop it

134. 2020, stop it

135. 2020, stop it

136. 2020, stop it

138. JavaScript was
invented in
Odessa
Dmitriy
Gusev
Summer. Sea. JavaScript.

139. https://habr.com/ru/post/137188/
https://medium.com/dailyjs/the-why-behind-the-wat-an-explanation-of-
javascripts-weird-type-system-83b92879a8db
https://blog.kevinchisholm.com/javascript/javascript-wat/
dotJS 2012 - Brian Leroux - WTFJS
JavaScript: The Good Parts
https://github.com/denysdovhan/wtfjs
https://wtfjs.com/
https://proglib.io/p/wtf-javascript-math/