Javascript Boolean Operator Logical NOT

Introduction

The Javascript logical NOT operator is represented by an exclamation point (!) and may be applied to any value in Javascript.

This operator returns a Boolean value, regardless of the data type it's used on.

The logical NOT operator first converts the operand to a Boolean value and then negates it.

The logical NOT behaves in the following ways:

  • If the operand is an object, false is returned.
  • If the operand is an empty string, true is returned.
  • If the operand is a nonempty string, false is returned.
  • If the operand is the number 0, true is returned.
  • If the operand is any number other than 0 (including Infinity), false is returned.
  • If the operand is null, true is returned.
  • If the operand is NaN, true is returned.
  • If the operand is undefined, true is returned.

The following example illustrates this behavior: 

console.log(!false);   // true 
console.log(!"blue");  // false 
console.log(!0);       // true 
console.log(!NaN);     // true 
console.log(!"");      // true 
console.log(!12345);   // false

The logical NOT operator can be used to convert a value into its Boolean equivalent.

By using two NOT operators in a row, you can simulate the behavior of the Boolean() casting function.

The end result is the same as using the Boolean() function on a value: 

console.log(!!"blue");  // true 
console.log(!!0);       // false 
console.log(!!NaN);     // false 
console.log(!!"");      // false 
console.log(!!12345);   // true



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