The document discusses equality comparisons in JavaScript and issues with type coercion when using the == and != operators. It shows examples where == returns unintuitive true values due to coercion, such as 0 == '' and 10 == '010'. The author advocates always using === and !== for comparisons, as === checks value and type strictly without coercion, avoiding performance and logic issues. The document also notes NaN is special, and isNaN() is preferred to check if a value is NaN.

1. Apples & Oranges?
Adventures in Equality Comparison & one of the ‘Bad Parts’
Kevin Munc - @muncman

2. Who needs transitivity?

3. Who needs transitivity?
‘’ == ‘0’

4. Who needs transitivity?
‘’ == ‘0’ false

5. Who needs transitivity?
‘’ == ‘0’ false okay...

6. Who needs transitivity?
‘’ == ‘0’ false okay...
0 == ‘’

7. Who needs transitivity?
‘’ == ‘0’ false okay...
0 == ‘’ true

8. Who needs transitivity?
‘’ == ‘0’ false okay...
0 == ‘’ true hmm...

9. Who needs transitivity?
‘’ == ‘0’ false okay...
0 == ‘’ true hmm...
0 == ‘0’

10. Who needs transitivity?
‘’ == ‘0’ false okay...
0 == ‘’ true hmm...
0 == ‘0’ true

11. Who needs transitivity?
‘’ == ‘0’ false okay...
0 == ‘’ true hmm...
0 == ‘0’ true uh...

12. The double-equals attempts
type coercion.

13. Crockford’s View
=== and !== are
the equality
comparison
operators.
== and != are the
‘evil twins’.

14. Not Truthy? Falsy?

15. Not Truthy? Falsy?
false == 0

16. Not Truthy? Falsy?
false == 0 true

17. Not Truthy? Falsy?
false == 0 true
false == ‘0’

18. Not Truthy? Falsy?
false == 0 true
false == ‘0’ true

19. For crying out loud.

20. For crying out loud.
10 == ’10’

21. For crying out loud.
10 == ’10’ true

22. For crying out loud.
10 == ’10’ true
10 == ‘010’

23. For crying out loud.
10 == ’10’ true
10 == ‘010’ true

24. Madness

25. Madness
10 == ’+10’

26. Madness
10 == ’+10’ true

27. Madness
10 == ’+10’ true
‘ trn’ == 0

28. Madness
10 == ’+10’ true
‘ trn’ == 0 true

29. Triple is the new black
Triple Equals === Strict Equals
When comparing objects, it checks identity. Otherwise, it
checks value - without coercion.
The implicit coercion of the ‘evil twins’ has a performance
cost, as well.
It’s better to make the coercion explicit if it is appropriate
for your comparison.

31. Bonus Question

32. Given:
NaN === NaN is false

33. Given:
NaN === NaN is false
How can we make this true?

34. Given:
NaN === NaN is false
How can we make this true?
NaN = 5
(it’s not a constant)
isNaN() is preferred for checks

35. Given:
NaN === NaN is false
How can we make this true?
NaN = 5
(it’s not a constant)
isNaN() is preferred for checks
undefined can also be changed

36. Questions? Comments?
The
Book
Photo Creds
http://covers.oreilly.com/images/9780596517748/lrg.jpg
http://www.flickr.com/photos/thedepartment/131206032/
http://www.flickr.com/photos/christinamatheson/108818379/
http://www.flickr.com/photos/thebusybrain/2492945625/
http://www.flickr.com/photos/kharied/3315558702/
http://www.flickr.com/photos/44974843@N04/457397
http://www.flickr.com/photos/teachernz/3222401608/