6.1 JS Booleans

The Boolean() Function

You can use the Boolean() function to find out if an expression (or a variable) is true:

Example 1: JS Booleans part 1

Boolean(10 > 9)        // returns true

Or even easier:

Example 2: JS Booleans part 2

(10 > 9)              // also returns true
10 > 9                // also returns true

Everything With a "Value" is True

Example 3: JS Booleans part 3

100

3.14

-15

"Hello"

"false"

7 + 1 + 3.14

Everything Without a "Value" is False

The Boolean value of 0 (zero) is false:

Example 4: JS Booleans value of 0

var x = 0;
Boolean(x);       // returns false

The Boolean value of -0 (minus zero) is false:

Example 5: JS Booleans value of -0

var x = -0;
Boolean(x);       // returns false

The Boolean value of "" (empty string) is false:

Example 6: JS Booleans value of ""

var x = "";
Boolean(x);       // returns false

The Boolean value of undefined is false:

Example 7: JS Booleans value of undefined

var x;
Boolean(x);       // returns false

The Boolean value of null is false:

Example 8: JS Booleans value of null

var x = null;
Boolean(x);       // returns false

The Boolean value of false is (you guessed it) false:

Example 9: JS Booleans value of false

var x = false;
Boolean(x);       // returns false

The Boolean value of NaN is false:

Example 10: JS Booleans value of NaN

var x = 10 / "H";
Boolean(x);       // returns false

Booleans Can be Objects

• Normally JavaScript booleans are primitive values created from literals:
• var x = false;
• But booleans can also be defined as objects with the keyword new:
• var y = new Boolean(false);

Example 11: JS Booleans and Boolean objects cannot be safely compared pt 1

var x = false;
var y = new Boolean(false);

// typeof x returns boolean
// typeof y returns object

Do not create Boolean objects. It slows down execution speed. The new keyword complicates the code. This can produce some unexpected results:

When using the == operator, equal booleans are equal:

Example 12: JS Booleans and Boolean objects cannot be safely compared pt 2

var x = false;             
var y = new Boolean(false);

// (x == y) is true because x and y have equal values

When using the === operator, equal booleans are not equal, because the === operator expects equality in both type and value.

Example 13: JS Booleans and Boolean objects cannot be safely compared pt 3

var x = false;             
var y = new Boolean(false);

// (x === y) is false because x and y have different types

Or even worse. Objects cannot be compared:

Example 14: JS Booleans and Boolean objects cannot be safely compared pt 4

var x = new Boolean(false);             
var y = new Boolean(false);

// (x == y) is false because objects cannot be compared

• Note the difference between (x==y) and (x===y).
• Comparing two JavaScript objects will always return false.