Home > Article > Web Front-end > faint! What does the interview question console.log(([][[]] + [])[+!![]]+([]+{})[+!![]+ + !![]]) output?
Interview questions console.log(([][[]] [])[ !![]] ([] {})[ !![] !![]]) output What? I encountered this interview question during the interview. The interview question examined type conversion, implicit type conversion, operators, etc. I couldn't answer it. It's not that I don't know how to answer it. It's just that I got dizzy just reading the question. However, it is indeed an interview question, so try to solve it.
First we have to clarify its execution order
First execute([][[]] [])
, first execute the [][[]]
inside. When calculating [][[]]
, it actually executes the key in the [] empty array. The value of []
[]
. An empty array has no elements. []
as the property name. In this case, since []
itself is an array, the JavaScript engine will try to convert it to a string. Since []
is an empty array, the result after conversion to a string is an empty string ""
. ""
in the empty array. Since this property does not exist in the empty array, the result is undefined
. So, the result of executing [][[]]
is undefined
.
Then ([][[]] [])
The next execution is (undefined [])
will perform implicit type conversion, and Convert undefined
to the string "undefined"
, convert [] to "", and then splice the two strings together. Therefore, the result is "undefined"
Then execute [!![]], !![] empty array is converted to a Boolean value of true, and the unary operation will Convert to numeric value, true is to convert true
into number 1
. The result is [1]
. So we can get ([][[]] [])[ !![]]
is undefined[1]
The result of this is the string 'n'
The next step is to execute ([] {})[ !![] !![]]
and then add the result of this part Add the above result
First execute ([] {})
, and calculate [] {}
. This triggers an implicit type conversion, converting the empty object to the string "[object Object]"
, and then concatenating the two strings together. Therefore, the result is '[object Object]'
.
Execute [!![] !![]] again, !![]
The result obtained after parsing is 1, so after executing this part, we get is to add the value 1 to 1 1
, and the result is [2]
.
Then the two parts combined are '[object Object]'[2]
, which is the third value of the string b
Finally, add the result 'n'
obtained in the previous part and the result 'b'
obtained in the latter part to get the final result 'nb'
Summary: If this problem cannot be solved for the time being, there may be several reasons. The first is that the execution sequence is not clear, and the second is that the execution sequence is not clear.[][[]]
This is actually to get the value of the empty array with the key []
, and because the key of the array is a string, []
will be converted to ''
cannot be found, so undefined is returned. Do you know this interview question now?
Recommended learning: "Web front-end development video tutorial"
The above is the detailed content of faint! What does the interview question console.log(([][[]] + [])[+!![]]+([]+{})[+!![]+ + !![]]) output?. For more information, please follow other related articles on the PHP Chinese website!