/javascriptss-addition-operator-demystified/ about dmitripavlutin.com-comments HOT 16 OPEN

Comment written by Azizul Haque on 06/17/2017 17:28:27

This article explains exactly what I was looking for. Thanks for nice explanation. Can you please explain why {} + 15 = 15 instead "[object Object]15" where 15 + {} = "15[object Object]" ?

from dmitripavlutin.com-comments.

Comment written by Dmitri Pavlutin on 06/19/2017 15:48:34

I'm glad you find the article helpful!
{} + 15 = 15 is 15 because JavaScript interprets { } as an empty block statement followed by +15. This construction is equivalent to:

{
   // empty block
}
+ 15

You can add a pair of parenthesis to explicitly define an object literal: ( {} ) + 15="[object Object]15".

The second case 15 + {}. JavaScript first transforms the object literal into a string, then transforms 15 into a string and concatenates: "15[object Object]".

from dmitripavlutin.com-comments.

Comment written by Azizul Haque on 06/19/2017 16:10:12

Thank you very much for your excellent explanation. Can you also do me a favour explaining why do JavaScript sometimes interprets {} as empty block and sometimes convert it into a string?

Thanks again

from dmitripavlutin.com-comments.

Comment written by Dmitri Pavlutin on 06/19/2017 16:17:40

Check here some details.

from dmitripavlutin.com-comments.

Comment written by luckyluckyx x on 06/25/2017 03:06:23

I learn a lot , thank you!

from dmitripavlutin.com-comments.

Comment written by Artur Mostowiak on 02/01/2018 20:40:26

This is a good explanation. Good job and thanks :)

from dmitripavlutin.com-comments.

Comment written by SAYED HASAN on 02/21/2018 04:51:38

Thanks dude

from dmitripavlutin.com-comments.

Comment written by Timur on 08/05/2018 08:30:56

Example 1: Number and string:

var result = 1 + "5"; // "15"

Explanation:

1 + "1" (The second operand is a string and based on rule 2 the number 1 becomes "1") // 1 + "5" ?

"1" + "1" (Strings concatenation) // "1" + "5" ?

"15"

from dmitripavlutin.com-comments.

Comment written by Tomasz Dudek on 07/06/2019 11:48:17

I study your articles (they great, the best I could found) but I still cannot understand how JS converts types. For example:

null + 8 // 8
because null is converted into 0
but
null == 0 // false
null is not converted... why?

Is types conversion dependent on operators?

from dmitripavlutin.com-comments.

Comment written by Dmitri Pavlutin on 07/07/2019 08:57:05

Thanks for reading my articles. I'm glad you find them useful.
`null == 0` is false because null is loosely equal == only to null or undefined.

Addition and equality are rather different operators, that's why the conversion rules are different.

Anyways, I always avoid comparing values of different types. That's the best rule to avoid misunderstandings.

from dmitripavlutin.com-comments.

If switch the operands in example 4 and do

{} + 15 // this returns 15 (the number!)

Why is that?

from dmitripavlutin.com-comments.

If switch the operands in example 4 and do

{} + 15 // this returns 15 (the number!)

Why is that?

See this comment.

from dmitripavlutin.com-comments.

1+2+"3" gives 33
while "1"+2+3 gives 123 why is that??

from dmitripavlutin.com-comments.

1+2+"3" gives 33
while "1"+2+3 gives 123 why is that??

What are your considerations on the question?

from dmitripavlutin.com-comments.

Great article, I recently encountered some code on leetcode that peaked my interest in how JavaScript handles the + and - operators when mixed with string numeric. The challenge was to replicate the atoi method. This idea was copied from a C++ example so the principles seem to work across multiple languages. I still have yet to find a clear description on how this works

const ar = ['9'];
let i = 0;
let result = 51;
let interim = result * 10 + (ar[i]); // 5109
result = result * 10 + (ar[i] - '0'); // 519
console.log(`\tcalculating ${interim} - '0' = ${result}`);

from dmitripavlutin.com-comments.

Interesting Article!
One more questions:
Since []+3 = 3 because the objects will turn into strings (''+3='3')

if I use an object literal as follows, why the result is a numeric value instead a string
{}+3 =3.

Great Blog BTW!

from dmitripavlutin.com-comments.