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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)

    Or even easier:

    Example

    (10 > 9)
    10 > 9

    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:

    let x = 0;
    Boolean(x);

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

    let x = -0;
    Boolean(x);

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

    let x = "";
    Boolean(x);

    The Boolean value of undefined is false:

    let x;
    Boolean(x);

    The Boolean value of null is false:

    let x = null;
    Boolean(x);

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

    let x = false;
    Boolean(x);

    The Boolean value of NaN is false:

    let x = 10 / "Hallo";
    Boolean(x);

    JavaScript Booleans as Objects

    Normally JavaScript booleans are primitive values created from literals:

    let x = false;

    But booleans can also be defined as objects with the keyword new:

    let y = new Boolean(false);

    Example

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

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

    Do not create Boolean objects.

    The new keyword complicates the code and slows down execution speed.

    Boolean objects can produce unexpected results:

    When using the == operator, x and y are equal:

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

    When using the === operator, x and y are not equal:

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

    Note the difference between (x==y) and (x===y).

    (x == y) true of false?

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

    (x === y) true of false?

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

    Comparing two JavaScript objects always return false.

    Complete Boolean Reference

    For a complete reference, go to our Complete JavaScript Boolean Reference.

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

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