Booleans

Boolean Values

When writing code we often need a data type that can represent the truth value, answer the Yes/No questions. JavaScript, among many other programming languages, has a Boolean data type. A JavaScript Boolean represents one of two values: true or false.

Note: true and false are in lower case. There are no quotation marks around them, since they are not strings.

Do not use true or false as variable names.

Boolean Expression

A Boolean expression is an expression that evaluates to a Boolean value.

Comparison Operators

The comparison operators are used in logical statements to compare two values. The result of the operation is a boolean value. Here are the common comparison operators:

== equal to != not equal > greater than
< less than
>= greater than or equal to
<= less than or equal to

Run the following examples and check the comparison results:

console.log(25 == 5*5)    // true
console.log(25 != 25)     // false
console.log(25 > 5**2)    // false
console.log(25 >= 5**2)   // true

console.log('hi' == 'Hi')         // false (stings are case sensitive)
console.log('Cat' != 'Chicken')   // true

p = 10
t = 1
console.log(p < t)       // false

Logical Operators

Logical operators allow a program to make a decision based on multiple conditions. There are three logical operators in JavaScript: && (and), || (or), ! (not)

The Truth Tables

&& (and): if both are true, the result is true

|| (or): if either of the two Boolean values is true, the result is true.

! (not): operates on only one Boolean value (or expression), result is the opposite.

Examples

console.log(false && true)            // false
console.log(4 == 2*2 && 2 == 3)       // false
console.log((5 < 10) || (10 >= 5*2))  // true

console.log('Cat' == 'Dog' && !(6==8 || 3==3))  // false
// false && !(false ||  true) --> false && false --> false