JavaScript boolean values explained

Learn how JavaScript boolean values work

Posted on May 03, 2022


JavaScript boolean values are used to represent truth logical values.

There are only two boolean type values: true or false.

The boolean values are commonly returned when you perform a comparison operator as follows:

50 > 20; // return true
10 === 15; // return false

You can assign a boolean value to variables like this:

let isAlive = true;

The boolean values are used when you need to perform a logical evaluation.

You can also use it to evaluate conditions required by an if statement.

For example, the age variable value must be greater than or equal to 18 to run the if statement block below:

let age = 15;

if (age >= 18) {
  console.log("You may enter");
} else {
  console.log("You shall not enter");
}

Values of another type in JavaScript always have a boolean type evaluation intrinsically.

For example, 0 equals false while other numbers are equal to true.

You can check the boolean representation of values by passing that value to the Boolean() function as shown below:

Boolean(0); // false
Boolean(1); // true
Boolean(-10); // true

Boolean(""); // false
Boolean("H"); // true

Boolean(null); // false
Boolean(undefined); // false

An empty string also returns false, while any other string returns true.

You can see the list of values that evaluate to true and false here:

JavaScript truthy falsy values explained

Finally, JavaScript also provides the Boolean constructor that you can use to create a Boolean object.

But keep in mind that the primitive value boolean is different than the object value Boolean.

Here’s an example of the two:

const primitiveBool = true;
const objBool = new Boolean(true);

console.log(typeof primitiveBool); // boolean
console.log(typeof objBool); // object

As you can see above, the type of primitiveBool evaluates to primitive boolean. On the other hand, the objBool value evaluates to an object.

You need to keep this in mind because an object will evaluate to true even when the object is a Boolean with a false value.

Consider the following example:

const objBool = new Boolean(false);

if (objBool){
    console.log(`Object value: ${objBool}`)
    // Object value: false
}

When you use a Boolean object for an if statement condition, the condition will always evaluate to true.

On the other hand, if you compare an object to a primitive boolean value, it will always return false:

const objBool = new Boolean(false);

console.log(objBool === true); // false
console.log(objBool === false); // false

When developing JavaScript applications, you are recommended to always use the primitive boolean type and avoid the Boolean object.

The Boolean() function can also be used when you need to find the primitive boolean value of an expression or value.

And that’s how the boolean values work in JavaScript. 👍

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