JavaScript Booleans

Table of contents

1. Complete Boolean Reference

JavaScript Booleans A JavaScript Boolean represents one of two values: true or false.

Boolean Values Very often, in programming, you will need a data type that can only have one of two values, like

YES / NO ON / OFF TRUE / FALSE For this, JavaScript has a Boolean data type. It can only take the values true or false.

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

Example Boolean(10 > 9) // returns true Or even easier:

Example (10 > 9) // also returns true 10 > 9 // also returns true Comparisons and Conditions The chapter JS Comparisons gives a full overview of comparison operators.

The chapter JS Conditions gives a full overview of conditional statements.

Here are some examples:

Operator Description Example == equal to if (day == “Monday”)

greater than	if (salary > 9000) <	less than	if (age < 18) The Boolean value of an expression is the basis for all JavaScript comparisons and conditions.

Everything With a “Value” is True Examples 100

3.14

-15

“Hello”

“false”

7 + 1 + 3.14 Everything Without a “Value” is False The Boolean value of 0 (zero) is false:

var x = 0; Boolean(x); // returns false The Boolean value of -0 (minus zero) is false:

var x = -0; Boolean(x); // returns false The Boolean value of “” (empty string) is false:

var x = “”; Boolean(x); // returns false The Boolean value of undefined is false:

var x; Boolean(x); // returns false The Boolean value of null is false:

var x = null; Boolean(x); // returns false The Boolean value of false is (you guessed it) false:

var x = false; Boolean(x); // returns false The Boolean value of NaN is false:

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 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 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 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 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.

Complete Boolean Reference

The reference contains descriptions and examples of all Boolean properties and methods.

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