Tilde ~

The ~ operator looks at the binary representation of the values of the expression and does a bitwise negation operation on it.

Any digit that is a 1 in the expression becomes a 0 in the result. Any digit that is a 0 in the expression becomes a 1 in the result.

~ Integer

The following example illustrates use of the bitwise NOT (~) operator on integer numbers.

let number = 3;
let complement = ~number;

Result of the complement number equals to -4;

ExpressionBinary valueDecimal value
300000000 00000000 00000000 000000113
~311111111 11111111 11111111 11111100-4

To simplify this, we can think of it as function f(n) = -(n+1).

let a = ~-2; // a is now 1
let b = ~-1; // b is now 0
let c = ~0;  // c is now -1
let d = ~1;  // d is now -2
let e = ~2;  // e is now -3

~~ Operator

Double Tilde ~~ will perform bitwise NOT operation twice.

The following example illustrates use of the bitwise NOT (~~) operator on decimal numbers.

To keep the example simple, decimal number 3.5 will be used, cause of it's simple representation in binary format.

let number = 3.5;
let complement = ~number;

Result of the complement number equals to -4;

ExpressionBinary valueDecimal value
300000000 00000000 00000000 000000113
~~300000000 00000000 00000000 000000113
3.500000000 00000011.13.5
~~3.500000000 000000113

To simplify this, we can think of it as functions f2(n) = -(-(n+1) + 1) and g2(n) = -(-(integer(n)+1) + 1).

f2(n) will leave the integer number as it is.

let a = ~~-2; // a is now -2
let b = ~~-1; // b is now -1
let c = ~~0;  // c is now 0
let d = ~~1;  // d is now 1
let e = ~~2;  // e is now 2

g2(n) will essentially round positive numbers down and negative numbers up.

let a = ~~-2.5; // a is now -2
let b = ~~-1.5; // b is now -1
let c = ~~0.5;  // c is now 0
let d = ~~1.5;  // d is now 1
let e = ~~2.5;  // e is now 2

Converting Non-numeric values to Numbers

~~ Could be used on non-numeric values. A numeric expression will be first converted to a number and then performed bitwise NOT operation on it.

If expression cannot be converted to numeric value, it will convert to 0.

true and false bool values are exceptions, where true is presented as numeric value 1 and false as 0

let a = ~~"-2";     // a is now -2
let b = ~~"1";      // b is now -1
let c = ~~"0";      // c is now 0
let d = ~~"true";   // d is now 0
let e = ~~"false";  // e is now 0
let f = ~~true;     // f is now 1
let g = ~~false;    // g is now 0
let h = ~~"";       // h is now 0

Shorthands

We can use ~ as a shorthand in some everyday scenarios.

We know that ~ converts -1 to 0, so we can use it with indexOf on array.

indexOf

let items = ['foo', 'bar', 'baz'];
let el = 'a';
if (items.indexOf('a') !== -1) {}

or

if (items.indexOf('a') >= 0) {}

can be re-written as

if (~items.indexOf('a')) {}

~ Decimal

The following example illustrates use of the bitwise NOT (~) operator on decimal numbers.

To keep the example simple, decimal number 3.5 will be used, cause of it's simple representation in binary format.

let number = 3.5;
let complement = ~number;

Result of the complement number equals to -4;

ExpressionBinary valueDecimal value
3.500000000 00000010.13.5
~3.511111111 11111100-4

To simplify this, we can think of it as function f(n) = -(integer(n)+1).

let a = ~-2.5; // a is now 1
let b = ~-1.5; // b is now 0
let c = ~0.5;  // c is now -1
let d = ~1.5;  // c is now -2
let e = ~2.5;  // c is now -3