When I execute
console.log( (4 + [] + 8) )I get the result of 48 and when I execute [] alone it gives 0. How does it work?
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j08691
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Mostafa Elnaggar
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its like `foo = null`, so `foo === null` and `typeof foo === 'object'` – DarkMukke Aug 17 '17 at 16:20
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Thank you for the explanation @DarkMukke – Mostafa Elnaggar Aug 17 '17 at 16:21
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1When you execute `[]` alone, it gives you an empty array. – rmalviya Aug 17 '17 at 16:22
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3`[].toString()` is `""` - i.e. an empty join. You will need to show how you get `0` from `[]` for an explanation. – Alex K. Aug 17 '17 at 16:22
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2`[]` with `+` (as a binary operator) will make it an empty string. So it basically becomes `4 + '' + 8` hence 48. – MinusFour Aug 17 '17 at 16:22
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When you treat it an integer it gives the value (0) but when you use it in an expression like (4 + [] + 8) the value of this expression is (48) @rmalviya – Mostafa Elnaggar Aug 17 '17 at 16:24
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Also see [What is the explanation for these bizarre JavaScript behaviours ...](https://stackoverflow.com/questions/9032856/what-is-the-explanation-for-these-bizarre-javascript-behaviours-mentioned-in-the) – Alex K. Aug 17 '17 at 16:25
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Thank you guys now I got it @Alex K. – Mostafa Elnaggar Aug 17 '17 at 16:26
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@MostafaElnaggar Give me an example of treating `[]` as an integer. I was talking about last statement in your question. – rmalviya Aug 17 '17 at 16:27
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`+[]` would be a number – Alex K. Aug 17 '17 at 16:29
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@AlexK. He (@MostafaElnaggar) used word `alone`. – rmalviya Aug 17 '17 at 16:30
2 Answers
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Because this is a sum of a number and an array, javascript is converting both to strings.
Therefore:
'4' + '' + '8' = '48' (notice that the result is a string, not a number)
If you add more elements to the array, it will work like this
4 + [1, 2] + 8 = '41,28'
This happens because arrays, by default, become strings by concatenating values with ,.
Another example
4 + [1, 2, 3, 4, 5] + 8 = 41,2,3,4,58
Note: If you try summing two arrays they will also become strings, as javascript doesn't have a native implementation for summing arrays.
[1, 2] + [3, 4] = '1,23,4'
Pedro Moreira
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Like explained in the comments.
When you use the + operator on an array to a variable of a different type, the js engine will call it as a string via [].toString().
Adding a number to a string also converts the numbers to a string.
DarkMukke
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You are right. but I did not want the credits, nor the upvotes, just get this more or less all over google question of the interesting page – DarkMukke Aug 17 '17 at 16:29