BooleansS2C Home « Booleans

Booleans are created using the global object constructor Boolean or exist in the form of the boolean primitives true and false.

The Boolean constructor is a wrapper for a boolean value and should not be confused with the true and false values of the Boolean primitives.

There are a some things to remember when creating Boolean objects and how the parameter passed to the Boolean constructor is converted to a boolean value:

  • If value is omitted or is 0, -0, null, false, NaN, undefined, or the empty string (''), the object has an initial value of false.
  • Any other values, including objects and the string 'false' create an object with an initial value of true.
  • Any values other than undefined and null evaluate to true when passed to a conditional statement.

The code below highlights the difference between the Boolean constructor and the boolean primitives true and false.



// Create a Boolean Object.
aBoolean = new Boolean(false);
if (aBoolean) {
  alert('set false, but evaluates true - Boolean Object'); // Executed
} else {
  alert('set false - Boolean Object'); // NOT executed
}

// Set a boolean primitive.
bBoolean = false;
if (bBoolean) {
  alert('set false, but evaluates true - boolean primitive'); // NOT executed
} else {
  alert('set false - boolean primitive'); // Executed
}

Press the button below to action the above code:


Reviewing The Code

Use the boolean primitives true and false when using conditional statements, and the Boolean constructor when you just want to wrap a boolean value.


Lesson 9 Complete

In this lesson we looked at booleans and some of their uses. This is the last lesson in the basics section of the site for JavaScript 1.5.

What's Next?

We begin the intermediate lessons with an investigation of arrays.

JavaScript 1.5 Reference

Boolean constructor
new special operator

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