What exactly does ~ do?

 

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  • What does a tilde do when it precedes an expression? 6 answers

    • It's the bitwise NOT operator. It will convert the operand to an 32-bit integer, then yields one's complement (inverts every bit) of that integer.

    Finally, ! will return true if and only only if the result of that operation is 0 .

    Some examples might help: 

      x |   x (bin) | ~x (bin)  |  ~x |   !~x
 -3 | 1111…1101 | 0000…0010 |   2 | false
 -2 | 1111…1110 | 0000…0001 |   1 | false
 -1 | 1111…1111 | 0000…0000 |   0 |  true
  0 | 0000…0000 | 1111…1111 |  -1 | false
  1 | 0000…0001 | 1111…1110 |  -2 | false

    In other words, 

    if ( !~text.indexOf('a') ) { }

    is equivalent to: 

    if ( text.indexOf('a') == -1 ) { }

    ~ is the bitwise negation operator[MDN]. It converts its operand to a 32-bit integer and swaps all the 1 s to 0 s and all the 0 s to 1 s.

    For example: 

    0000 0000 0000 0000 0000 0000 0000 0000 = 0
1111 1111 1111 1111 1111 1111 1111 1111 = ~0 = -1

    Instead of doing text.indexOf(str) !== -1) you can use the tricky !~text.indexOf(str) , because ~1 === 0 and !0 === true .

    ~ is the unary negation operator. Basically converts the operand to a 32-bit integer and then flips every bit of the integer. 

    ~12 =
~(00000000 00000000 00000000 00001100) =
 (11111111 11111111 11111111 11110011) =
-13
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