JavaScript Expression

 

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  • Why does ++[[]][+[]]+[+[]] return the string “10”? 8 answers

    • First break out your code to this: !![] which returns true (!! is to convert to boolean) and now + converts to number so +!![] returns 1.

    ![] converts to false so +![] returns 0.

    ~[] returns -1 and ~![] also returns -1 .

    ~!![] returns -2 .

    Now, -~!![] returns 2 and -~![] returns 1.

    So, combining them all returns 10162014.

    All about you to know is ~, !, +, & -

    ![] = false; # as an expression, it's false due to the ! operatory [] = true; # as an expression, it's defined, so it's true

    +!![] = 1; because +true = 1; +![] = 1; because +true = 0 , because using a + operator in JS converts the boolean to an integer ref

    So what he's done is basically constructed a numerical value using boolean to integer conversion, and some grouping.

    [+!![]]+[+![]]+[+!![]] : [] is an empty array, which is truthy. ![] is thus false, !![] is true. +true forces it to a number, as 1 . Similarly for +![] as 0 via false .

    [-~!![]+-~!![]-~!![]] : ~ is a two's complement operator; ~1 is -2 . Thus, this evaluates as -(-2)+-(-2)+-(-2) , which is 6 .

    The remaining addends are analogous.

    array + array will convert arrays to strings; thus [1]+[0]+[1]+[6]... will give the string "1016..."

    The plus at start will convert it to a number.

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