Understanding Boolean in JavaScript

In JavaScript, a boolean is a basic (primitive) data type. It can only have two values:

true (yes)
false (no)

Booleans are used to control the flow of a program, especially in conditions like if, else, while, and switch.

Example: Boolean Variables

    var YES = true;
    var NO = false;

How Booleans Control Program Flow

    var YES = true;
    var NO = false;

    if (YES) {
    alert("This code block will run."); // This will happen
    }

    if (NO) {
    alert("This code block will NOT run."); // This will NOT happen
    }

Boolean from Comparison

When you compare values, the result is always true or false.

    var a = 10, b = 20;

    var result = 1 > 2;     // false
    result = a < b;         // true
    result = a > b;         // false
    result = a + 20 > b + 5; // true

Boolean() Function

JavaScript has a Boolean() function that converts other values to either true or false.

Returns `true` for:

Any non-zero number
Any non-empty string
An object or array

    var b1 = Boolean('Hello'); // true
    var b2 = Boolean(10);      // true
    var b3 = Boolean([]);      // true

Returns `false` for:

0, -0
null
false
NaN (Not a Number)
undefined
'' (empty string)

    var b1 = Boolean('');     // false
    var b2 = Boolean(0);      // false
    var b3 = Boolean(null);   // false

    var a;
    var b4 = Boolean(a);      // false

Boolean Object (`new Boolean()`)

You can also create a Boolean object using new Boolean().

    var bool = new Boolean(true);
    alert(bool); // shows "true"

But here's a trick:

Even if you create a Boolean object with false, it still acts like true in conditions!

    var bool = new Boolean(false);

    if (bool) {
    alert("This will still run!");
    }

Boolean vs Boolean Object

Type	Created with	Type	Example
`boolean` (primitive)	`true` or `false`	`"boolean"`	`typeof true` ? `"boolean"`
`Boolean` (object)	`new Boolean()`	`"object"`	`typeof new Boolean(true)` ? `"object"`

Boolean Methods

These methods can be used with booleans:

Method	What It Does	Example
`toString()`	Converts boolean to `"true"` or `"false"`	`(1 > 2).toString(); // "false"`
`toLocaleString()`	Like `toString()`, but uses browser settings	`(1 > 2).toLocaleString(); // "false"`
`valueOf()`	Returns the real value (`true` or `false`)	`(1 > 2).valueOf(); // false`

Summary

true and false are called booleans.
They're used in conditions to control what code runs.
Boolean() converts other types into true or false.
new Boolean() creates an object (be careful — even new Boolean(false) is "truthy").
Use typeof to check the type ("boolean" or "object").
Boolean values have helpful methods like toString() and valueOf().