booleans

In this module we will study booleans.

File Location

You should be located in the following file:

   javascript-library
        └── 0-PreWork
            └── 1-HTML-Basics
            └── 2-CSS-Basics
            └── 3-JavaScript-Basics
                04-booleans.js       <----You will be working in this file in this module.

Description

Simply put, boolean values allow us to set a variable to a true or false value. Very often, in programming, you will need a data type that can only have one of two values, such as:

YES / NO
ON / OFF
TRUE / FALSE

For this, JavaScript has a Boolean data type. It can only take the values true or false.

Examples

Here's how we can declare a boolean variable in JavaScript. Here we both declare the variable and initialize it with a boolean value.

var isLoggedIn = true;
var isAuthenticated = true;
var hasLoggedInToday = false;
var hasToken = false;

Comparison Operators

Booleans are often used to compare two values for equality, inequality, or difference:

Operator	Meaning
==	Equality
===	Strict Equality
!=	Inequality
!==	Strict Inequality
>	Greater than
>=	Greater than or equal
<	Less than
<=	Less than or equal

Printing Values

We can play with the boolean operators and print a few items out:

console.log(2 > 1); //true
console.log(3 < 2); //false

var test = 2 >= 3; //What will this print?
console.log(test);
console.log("Two is greater than one? " + (2 > 1));
console.log(3 >= 1);

Other Operations

Some other operations to see when dealing with equality.

Here's an important rule about == versus ===.

== checks to see if the values are the same. Not the type. === checks to see if the values and the equality are the same.

Expression	Result	Reason
2 == "2";	True	This checks for equality, not type.
1 == "1";	True	This checks for equality, not type.
2 === "2";	False	Equality is the same, but type is different.
2 === 2;	True	Equality and type are the same.
"Password12!!" === "Password12!!"	True	Equality and type are the same.

More Practice

Think it through: What would be the value for the following three?

"Password12!" === "Password12!!"
1 !== 2                    //=> true
10 !== 10                //=> false

Logical Operators

These are important and fairly easy to memorize. Essentially, && is the equivalent of and, || means or, and ! or bang means not.

We gave some hard thinking examples to get your brain working with it:

&& stands for AND Example: 4 > 0 && -2 < 0 || stands for OR Example: 4 > 0 || -2 > 0 ! stands for NOT Example: !(posNum < 0)

Here are a few more examples that you can print:

console.log("&& :", 2===2 && 1===1 ); //true because?
console.log("|| :", 2===2 || 2===1 ); //true because?
console.log("!=", 2 != 1) //true because?

Common Job Interview Question

What is the difference between == & === in JavaScript?