The tilde ( ~ ) operator in JavaScript
From the JavaScript Reference on MDC,
~ (Bitwise NOT)
Performs the NOT operator on each bit. NOT
a
yields the inverted value (a.k.a. one’s complement) ofa
. The truth table for the NOT operation is:
a NOT a 0 1 1 0 Example:
9 = 00000000000000000000000000001001 (base 2)
--------------------------------
~9 = 11111111111111111111111111110110 (base 2) = -10 (base 10)Bitwise NOTing any number x yields -(x + 1). For example, ~5 yields -6.
Now lets look at the Logical NOT(!)
! (Logical NOT)
Returns false if its single operand can be converted to true; otherwise, returns true.
Mixing the two NOT operators together can produce some interesting results:
!~(-2) = false
!~(-1) = true
!~(0) = false
!~(1) = false
!~(2) = false
For all integer operands except -1, the net operand after applying the ~ operator for the ! operator would be truthy in nature resulting in FALSE.
-1 is special because ~(-1) gives 0 which is falsy in JavaScript. Adding the ! operator gives us the only TRUE.
When to use this special case ?
A lot of times in JavaScript String manipulation, you are required to search for a particular character in a string. For example,
var str = 'posterous'; if ( str.search('t') >= 0 ) {
// character t found
}
else{
// not found
}
We can use the operators instead of the comparison operators, like this:
var str = 'posterous'; if ( !~str.search('t') ) {
// character 't' not found branch
}
else{
// found branch
}
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