/the-legend-of-javascript-equality-operator/ about dmitripavlutin.com-comments HOT 20 OPEN

Comment written by Eric on 01/14/2016 23:40:26

Well documented!

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Comment written by Charles Robertson on 03/07/2016 21:28:30

Brilliant article. Thank you:

[0] == 0

-> 0 == 0 // true

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Comment written by Dmitri Pavlutin on 03/08/2016 05:06:25

You're welcome.
Yes, the evaluation is correct.

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Comment written by Peshmerge on 03/29/2016 14:40:55

[0] == 0, object will be converted to primitive data type so it will be like this " 0==0 " and that is true :)
Very helpful article. Thank you very much :)

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Comment written by Dmitri Pavlutin on 04/11/2016 08:55:53

I'm glad that you like it. Thanks.

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Comment written by Deepak Sai on 04/24/2016 18:47:44

Dmitri ,,, thanks for you and your time for sharing this, really a good JS
article ...

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Comment written by Harjot Sahota on 04/28/2016 06:12:38

Very clear explanation. Thank you.

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Comment written by William Young on 04/28/2016 10:39:29

[0] == 0
"0"==0
0==0
True

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Comment written by Ravinder Kumar on 05/06/2016 07:28:05

[0] == 0;
'0'==0;
0==0;
0===0; //true;

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Comment written by Ravinder Kumar on 05/06/2016 07:30:20

You really helped me to understand 'stone age' well. Done a great job.

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Comment written by Dmitri Pavlutin on 05/06/2016 07:32:05

I'm glad the explanation helped you. Thanks!

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Comment written by loopmode on 05/15/2016 10:07:17

"If one operand is number and another is a string, convert the string to number. Compute the comparison again"

Seems inefficient, or am I missing something? I wonder why not convert the number to string, which works always, while string to number can obviously fail in n cases..

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Comment written by Dmitri Pavlutin on 05/15/2016 15:47:41

Interesting question.
The equality is transforming operators to numbers (if one of it is a number) to deal with different formats that a number can have. For example:

'1.0' == 1

It makes sense to transform '1.0' into a number, then compare 1.0 === 1 which is true.
If transforming both operands to string, '1.0' == '1' is false, which is not quite expected.

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Comment written by Marek on 05/18/2016 12:16:29

Do if statements work differently ? Having {} == true // false why does if ({}) evaluate to true?

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Comment written by Dmitri Pavlutin on 05/18/2016 13:01:31

Hi Marek.
Yes, if ({} == true) { } and if ({}) { } are evaluated differently by JavaScript.
The first case you can find described in the example 7. It evaluates to false.
The second case doesn't involve any comparison operators. The condition is passed because the object literal {} is a truthy value.
Falsy values in JavaScript are considered '', null, undefined, NaN, 0, false. All other ones are truthy, including objects (like {}), true, 1, etc.
Thanks for your interesting question.

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Comment written by Marek on 05/19/2016 06:36:16

Thanks for the quick reply! Now everything's clear.

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Comment written by Suresh Raj on 06/12/2016 04:49:28

Hi Dmitri, another great in depth article. I have doubt in "The equality operator example 2" section,
how js transform ' ' into number 0 ? Because parseInt('') return NaN.

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Comment written by Dmitri Pavlutin on 06/12/2016 05:25:55

Hi Suresh. In equality, JavaScript uses Number() function to transform a string into an integer. This way Number('') is 0.

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Comment written by Artur Mostowiak on 02/01/2018 21:14:41

Also good and short explanation. Keep up with a good work :)

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Comment written by Artur Mostowiak on 10/28/2019 12:53:32

Nice

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