Clean Code in JavaScript

The logical NOT operator

The NOT operator is a unary operator. It accepts only a single operand and converts that operand into its Boolean representation, then inverts it, so that truthy items become false and falsy items become true:

!1;    // => false!true; // => false!'hi;  // => false!0;    // => true!'';   // => true!true; // => false

Internally, the NOT operator will perform the following:

1. Cast the operand to a Boolean (Boolean(operand))
2. If the resulting value is true, then return false; otherwise, return true

As discussed in the Conversion to a Boolean section in the last chapter, a typical idiom for converting a value to its Boolean representation is the double NOT (that is, !!value) as this effectively reverses the truthiness or falsiness ...