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
Or even easier:
Example
10 > 9 // also returns true
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
3.14
-15
"Hello"
"false"
7 + 1 + 3.14
Everything Without a "Value" is False
The Boolean value of 0 (zero) is false:
Boolean(x); // returns false
The Boolean value of -0 (minus zero) is false:
Boolean(x); // returns false
The Boolean value of "" (empty string) is false:
Boolean(x); // returns false
The Boolean value of undefined is false:
Boolean(x); // returns false
The Boolean value of null is false:
Boolean(x); // returns false
The Boolean value of false is (you guessed it) false:
Boolean(x); // returns false
The Boolean value of NaN is false:
Boolean(x); // returns false
Booleans Can be 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 y = new Boolean(false);
// typeof x returns boolean
// typeof y returns object
Do not create Boolean objects. It slows down execution speed.
The new keyword complicates the code. This can produce some unexpected results:
When using the == operator, equal booleans are equal:
Example
let y = new Boolean(false);
// (x == y) is true because x and y have equal values
When using the === operator, equal booleans are not equal, because the === operator expects equality in both type and value.
Example
let y = new Boolean(false);
// (x === y) is false because x and y have different types
Or even worse. Objects cannot be compared:
Example
let y = new Boolean(false);
// (x == y) is false because objects cannot be compared
Note the difference between (x==y) and (x===y).
Comparing two JavaScript objects will always return false.
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