Grokking JavaScript Fundamentals
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JavaScript - Boolean
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In JavaScript, the Boolean object is a wrapper for a boolean value, either true or false. Booleans are often used in conditions to decide the flow of control in programming. Understanding how to work with Boolean objects and values is fundamental in creating logical conditions and expressions that drive decision-making processes in your code.

While directly using Boolean objects is less common than using primitive boolean values, understanding how they work, especially how different values are converted to true or false, is crucial for effective JavaScript programming.

Syntax

The Boolean object can be created using the Boolean() constructor, which converts a given value to its boolean equivalent:

var trueValue = new Boolean(true);
var falseValue = new Boolean(false);
  • Using the new Boolean(value); syntax, you can create a Boolean object. The value passed to the constructor determines the truthiness or falsiness of the resulting Boolean object.

Note: It's important to note that all values passed to the Boolean() constructor, except 0, NaN, "", null, undefined, and false, create an object that evaluates to true.

Methods

Here is a list of the method associated with the Boolean object.

Method NameDescription
valueOf()Returns the primitive value of a Boolean object as a boolean data type (true or false).

Example

Let's look at an example using the valueOf() method:

Javascript
Javascript
. . . .
  • A Boolean object myBool is created with the value true.
  • myBool.valueOf() returns the primitive value of myBool, which is the boolean value true.

Falsy Boolean Values

In JavaScript, certain values are considered "falsy," meaning they are treated as false in Boolean contexts. These include:

  • false
  • 0 (zero)
  • "" (empty string)
  • null
  • undefined
  • NaN

All other values are considered "truthy" and will evaluate to true in Boolean contexts.

Example: Falsy Boolean Values

Javascript
Javascript
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  • In this example, we use an if statement to test a series of values: false, 0, "" (empty string), null, undefined, and NaN.
  • The || (logical OR) operator is used to chain these values together. In a Boolean context, JavaScript evaluates each operand from left to right and stops at the first truthy value. If no truthy value is found, the last value is returned.
  • Since all these values are falsy, the condition in the if statement evaluates to false, and the code block associated with the if statement is skipped.
  • The program then executes the else block, printing "All values are falsy." to the console.

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