JavaScript Logic

JavaScript boolean (logical) represents one of two values:true or false.

Boolean values

In programming, you often need a data type that can only have one of two values, such as

  • YES / NO
  • ON / OFF
  • TRUE / FALSE

For this reason, JavaScript provides aBooleandata types. It only accepts values true or false.

Boolean() function

You can use Boolean() A function to determine whether an expression (or variable) is true:

Example

Boolean(10 > 9)        // returns true

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Or even simpler:

Example

(10 > 9)              // also returns true
10 > 9                // also returns true

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Comparison and Condition

This chapter of JS Comparison lists the complete comparison operators.

This chapter of JS Conditions lists the complete 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 of JavaScript comparison and conditional logic.

All values that have a 'truthy' value are True

Example

100
3.14
-15
"Hello"
"false"
7 + 1 + 3.14
5 < 6

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All values that do not have a 'truthy' value are False

0 (zero)The boolean value is false:

var x = 0;
Boolean(x);       // returns false

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-0 (negative zero)The boolean value is false:

var x = -0;
Boolean(x);       // returns false

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"" (empty value)The boolean value is false:

var x = "";
Boolean(x);       // returns false

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undefined The boolean value is false:

var x;
Boolean(x);       // returns false

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null The boolean value is false:

var x = null;
Boolean(x);       // returns false

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false The boolean value (as you might have guessed) is false:

var x = false;
Boolean(x);       // returns false

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NaN The boolean value is false:

var x = 10 / "H";
Boolean(x);       // returns false

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Boolean can be an object

Typically, JavaScript booleans are created from primitive values:

var x = false

But boolean can also be defined through the keyword new Defined as an object:

var y = new Boolean(false)

Example

var x = false;
var y = new Boolean(false);
// typeof x returns boolean
// typeof y returns object

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Do not create boolean objects. It will slow down the execution speed.

new The keyword can complicate the code and produce some unexpected results:

when using == operator, equal booleans are equal:

Example

var x = false;             
var y = new Boolean(false);
// (x == y) is true because x and y have equal values

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when using === When using the operator, equal booleans are not equal because === The operator needs to be equal in both type and value.

Example

var x = false;             
var y = new Boolean(false);
// (x === y) is false because x and y have different types

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Or even worse. Objects cannot be compared:

Example

var x = new Boolean(false);             
var y = new Boolean(false);
// (x == y) is false because objects cannot be compared

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Comparing two JavaScript objects will always return false.

Complete Boolean Reference Manual

For the complete reference manual, please visit our JavaScript Boolean Reference Manual.

The reference manual includes descriptions and examples of all boolean properties and methods.