What is an exclamation point in JavaScript?

Question

What does an exclamation mark before a function do?

Example:

return !loadDynamicBlock();

'tis logic NOT operator - !true==false, !false==true, if (!false) == if (true). — totallyNotLizards, Nov 04 '11 at 15:51

Dave Newton · Accepted Answer · 2011-11-26T15:18:38.020

25

A ! negates an expression.

In your example, if loadDynamicBlock() returned true, the function calling it would return false, and vice-versa: !true == false

It can also be used to create actual booleans from JavaScript's ideas of truthy and falsy.

var a = 5;
!!(a - 5) === false;
!!(a + 5) === true;

edited Nov 26 '11 at 15:18

answered Nov 04 '11 at 15:50

Dave Newton

score 6 · Answer 2 · answered Nov 04 '11 at 15:51

6

The ! in Javascript inverts a boolean expression.

answered Nov 04 '11 at 15:51

JaredPar

2 Answers2