What is an exclamation point in JavaScript?

Question

What does an exclamation mark before a function do?

Example:

return !loadDynamicBlock();

Answer 1

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;

Answer 2

The ! in Javascript inverts a boolean expression.