Slide 1

Logical AND (&&)

The logical AND (&&) operator (logical conjunction) for a set of operands is true if and only if all of its operands are true. It is typically used with Boolean (logical) values. When it is, it returns a Boolean value. However, the && operator actually returns the value of one of the specified operands, so if this operator is used with non-Boolean values, it will return a non-Boolean value.

  const a = 3;
  const b = -2;

  console.log(a > 0 && b > 0);
  // expected output: false

Syntax

  expr1 && expr2

Slide 2

Examples

Using AND

The following code shows examples of the && (logical AND) operator.

 a1 = true  && true       // t && t returns true
 a2 = true  && false      // t && f returns false
 a3 = false && true       // f && t returns false
 a4 = false && (3 == 4)   // f && f returns false
 a5 = 'Cat' && 'Dog'      // t && t returns "Dog"
 a6 = false && 'Cat'      // f && t returns false
 a7 = 'Cat' && false      // t && f returns false
 a8 = ''    && false      // f && f returns ""
 a9 = false && ''         // f && f returns false

Slide 3

Conversion rules for booleans

Converting AND to OR

The following operation involving booleans:

 bCondition1 && bCondition2

is always equal to:

 !(!bCondition1 || !bCondition2)

Converting OR to AND

The following operation involving booleans:

 bCondition1 || bCondition2

is always equal to:

 !(!bCondition1 && !bCondition2)