Is it safe to change == to === according to jshint's error detection without further checking

Question

I'm checking JavaScript code based on JSHint tool. This tool detected lots of errors about using "===" instead of "==". My question is that Is it safe to just follow what JSHint said? Do I need to check further (about their types and values) before replacing == by === ? Thanks!

You may need to check, yes. – powerbuoy Apr 09 '13 at 11:48 — powerbuoy, Apr 09 '13 at 11:48

score 2 · Answer 1 · edited May 23 '17 at 11:49

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Yup, you should.

If you wrote your code without having into account type coercion some errors you didn't expect could happen, like

'' == '0'           // false
0 == ''             // true
0 == '0'            // true

false == 'false'    // false
false == '0'        // true

false == undefined  // false
false == null       // false
null == undefined   // true

' \t\r\n ' == 0     // true

edited May 23 '17 at 11:49

Community

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answered Apr 09 '13 at 11:50

nicosantangelo

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"the lack of transitivity is alarming" :-) – Christoph Apr 09 '13 at 11:51

score 1 · Answer 2 · answered Apr 09 '13 at 11:48

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My question is that Is it safe to just follow what JSHint said?

No. You might be depending on the type coercion that == gives.

Do I need to check further (about their types and values) before replacing == by === ?

Yes.

answered Apr 09 '13 at 11:48

Quentin

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score 1 · Answer 3 · answered Apr 09 '13 at 11:49

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""==0 // true

""===0 // false

so you cant just blindly change all your code and expect it to work like before. That's why your code should have unit tests. So you know what doesnt work anymore.

answered Apr 09 '13 at 11:49

mpm

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According to Douglas Crockford (quoted without attribution by @Nicosunshine), `""==0` is `false`... – Tim Pietzcker Apr 09 '13 at 12:09
@TimPietzcker I left the link to the answer where I copied the info :). Maybe I should have made it more clear, my bad – nicosantangelo Apr 09 '13 at 13:19

score 1 · Accepted Answer · answered Apr 09 '13 at 11:54

Replacing == by === is a recommendation because it makes the code easier to predict and less error prone. Douglas Crockford proposes to never use ==. However it is just his opinion.

Actually, if you have such checks in your code and know what you are doing (that the types will get coerced) and perhaps are even relying on that behaviour, it is absolutely okay to work with those comparisons. You can just uncheck the "Warning about unsafe comparison".

If you want to replace those comparisons you definitely have to check if your code keeps working as intended.

Is it safe to change == to === according to jshint's error detection without further checking

4 Answers4