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JavaScript Operators Reference


JavaScript operators are used to assign values, compare values, perform arithmetic operations, and more.


JavaScript Arithmetic Operators

Arithmetic operators are used to perform arithmetic between variables and/or values.

Given that y = 5, the table below explains the arithmetic operators:

Operator Description Example Result in y Result in x
+ Addition x = y + 2 y = 5 x = 7
- Subtraction x = y - 2 y = 5 x = 3
* Multiplication x = y * 2 y = 5 x = 10
/ Division x = y / 2 y = 5 x = 2.5
% Modulus (division remainder) x = y % 2 y = 5 x = 1
++ Increment x = ++y y = 6 x = 6
x = y++ y = 6 x = 5
-- Decrement x = --y y = 4 x = 4
x = y-- y = 4 x = 5
JavaScript Arithmetic Tutorial.

JavaScript Assignment Operators

Assignment operators are used to assign values to JavaScript variables.

Given that x = 10 and y = 5, the table below explains the assignment operators:

Operator Example Same As Result in x Try it
= x = y x = y x = 5
+= x += y x = x + y x = 15
-= x -= y x = x - y x = 5
*= x *= y x = x * y x = 50
/= x /= y x = x / y x = 2
%= x %= y x = x % y x = 0
JavaScript Assignment Tutorial.

JavaScript String Operators

The + operator, and the += operator can also be used to concatenate (add) strings.

Given that text1 = "Good ", text2 = "Morning", and text3 = "", the table below explains the operators:

Operator Example text1 text2 text3
+ text3 = text1 + text2 "Good " "Morning"  "Good Morning"
+= text1 += text2 "Good " "Morning" ""

Comparison Operators

Comparison operators are used in logical statements to determine equality or difference between variables or values.

Given that x = 5, the table below explains the comparison operators:

Operator Description Comparing Returns
== equal to x == 8 false
x == 5 true
=== equal value and equal type x === "5" false
x === 5 true
!= not equal x != 8 true
!== not equal value or not equal type x !== "5" true
x !== 5 false
> greater than x > 8 false
< less than x < 8 true
>= greater than or equal to x >= 8 false
<= less than or equal to x <= 8 true
JavaScript Comparisons Tutorial.

Conditional (Ternary) Operator

The conditional operator assigns a value to a variable based on a condition.

Syntax Example
variablename = (condition) ? value1:value2 voteable = (age < 18) ? "Too young":"Old enough";

Example explained: If the variable "age" is a value below 18, the value of the variable "voteable" will be "Too young", otherwise the value of voteable will be "Old enough".


Logical Operators

Logical operators are used to determine the logic between variables or values.

Given that x = 6 and y = 3, the table below explains the logical operators:

Operator Description Example
&& and (x < 10 && y > 1) is true
|| or (x === 5 || y === 5) is false
! not !(x === y) is true

JavaScript Bitwise Operators

Bit operators work on 32 bits numbers. Any numeric operand in the operation is converted into a 32 bit number. The result is converted back to a JavaScript number.

Operator Description Example Same as Result Decimal
& AND x = 5 & 1 0101 & 0001 0001  1
| OR x = 5 | 1 0101 | 0001 0101  5
~ NOT x = ~ 5  ~0101 1010  10
^ XOR x = 5 ^ 1 0101 ^ 0001 0100  4
<< Left shift x = 5 << 1 0101 << 1 1010  10
>> Right shift x = 5 >> 1 0101 >> 1 0010   2


The typeof Operator

The typeof operator returns the type of a variable, object, function or expression:

Example

typeof "John"                 // Returns string
typeof 3.14                   // Returns number
typeof NaN                    // Returns number
typeof false                  // Returns boolean
typeof [1, 2, 3, 4]           // Returns object
typeof {name:'John', age:34}  // Returns object
typeof new Date()             // Returns object
typeof function () {}         // Returns function
typeof myCar                  // Returns undefined (if myCar is not declared)
typeof null                   // Returns object

Please observe:

  • The data type of NaN is number
  • The data type of an array is object
  • The data type of a date is object
  • The data type of null is object
  • The data type of an undefined variable is undefined

The delete Operator

The delete operator deletes a property from an object:

Example

var person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};
delete person.age;   // or delete person["age"];

The delete operator deletes both the value of the property and the property itself.

After deletion, the property cannot be used before it is added back again.

The delete operator is designed to be used on object properties. It has no effect on variables or functions.

Note: The delete operator should not be used on predefined JavaScript object properties. It can crash your application.


The in Operator

The in operator returns true if the specified property is in the specified object, otherwise false:

Example

// Arrays
var cars = ["Saab", "Volvo", "BMW"];
"Saab" in cars          // Returns false (specify the index number instead of value)
0 in cars               // Returns true
1 in cars               // Returns true
4 in cars               // Returns false (does not exist)
"length" in cars        // Returns true  (length is an Array property)

// Objects
var person = {firstName:"John", lastName:"Doe", age:50};
"firstName" in person   // Returns true
"age" in person         // Returns true

// Predefined objects
"PI" in Math            // Returns true
"NaN" in Number         // Returns true
"length" in String      // Returns true

The instanceof Operator

The instanceof operator returns true if the specified object is an instance of the specified object:

Example

var cars = ["Saab", "Volvo", "BMW"];

cars instanceof Array;          // Returns true
cars instanceof Object;         // Returns true
cars instanceof String;         // Returns false
cars instanceof Number;         // Returns false

The void Operator

The void operator evaluates an expression and returns undefined. This operator is often used to obtain the undefined primitive value, using "void(0)" (useful when evaluating an expression without using the return value).

Example

<a href="javascript:void(0);">
  Useless link
</a>

<a href="javascript:void(document.body.style.backgroundColor='red');">
  Click me to change the background color of body to red
</a>