JavaScript Operator Reference Manual

JavaScript operators are used for assignment, comparison of values, execution of arithmetic operations, etc.

See also:

Tutorial:JavaScript Operators

Tutorial:JavaScript Operator Precedence

JavaScript Arithmetic Operators

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

Given y = 5The following table explains the arithmetic operators:

Operator Description Example The result in y The result in x Try it
+ Addition x = y + 2 y = 5 x = 7 Try it
- Subtraction x = y - 2 y = 5 x = 3 Try it
* Multiplication x = y * 2 y = 5 x = 10 Try it
/ Division x = y / 2 y = 5 x = 2.5 Try it
% Modulus (remainder of division) x = y % 2 y = 5 x = 1 Try it
++ Increment x = ++y y = 6 x = 6 Try it
x = y++ y = 6 x = 5 Try it
-- Decrement x = --y y = 4 x = 4 Try it
x = y-- y = 4 x = 5 Try it

For knowledge about arithmetic operators, please read our JavaScript Arithmetic Tutorial.

JavaScript Assignment Operators

Assignment operators are used to assign values to JavaScript variables.

Given x = 10 and y = 5The following table explains the assignment operators:

Operator Example Is equivalent to The result in x Try it
= x = y x = y x = 5 Try it
+= x += y x = x + y x = 15 Try it
-= x -= y x = x - y x = 5 Try it
*= x *= y x = x * y x = 50 Try it
/= x /= y x = x / y x = 2 Try it
%= x %= y x = x % y x = 0 Try it

For knowledge about assignment operators, please read our JavaScript Assignment Tutorial.

JavaScript String Operators

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

Given text1 = "Good "、text2 = "Morning"as well as text3 = ""The following table explains this operator:

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

Comparison operators

Use comparison operators in logical statements to determine the equality or difference between variables or values.

Given x = 5The following table explains the comparison operators:

Operator Description Comparison Return Try it
== Equal to x == 8 false Try it
x == 5 true Try it
=== Equal values and equal types x === "5" false Try it
x === 5 true Try it
!== Not equal x != 8 true Try it
!== Unequal values or unequal types x !== "5" true Try it
x !== 5 false Try it
> Greater than x > 8 false Try it
< Less than x < 8 true Try it
>= Greater than or equal to x >= 8 false Try it
<= Less than or equal to x <= 8 true Try it

For knowledge about comparison operators, please read our JavaScript Comparison Tutorial.

Conditional (ternary) operator

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

Syntax

variablename = (condition) ? value1:value2

Example

voteable = (age < 18) ? 'Too young':'Old enough';

Try It Yourself

Example explanation:

If the value of the variable 'age' is less than 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 x = 6 and y = 3The following table explains the logical operators:

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

JavaScript bitwise operators

Bitwise operators can handle 32-bit numbers. Any number operand in this operation will be converted to a 32-bit number. The result will be converted back to a JavaScript number.

Operator Description Example Is equivalent to 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 ^ 0100 4
<< Left shift x = 5 << 1 0101 << 1 1010 10
>> Right shift x = 5 >> 1 0101 >> 1 0010 2

The above example uses a 4-bit unsigned example. However, JavaScript uses 32-bit signed numbers.

Therefore, in JavaScript, ~5 will not return 10, but -6.

~00000000000000000000000000000101 will return 11111111111111111111111111111010

typeof operator

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

Example

typeof "Bill"                 // Returns string
typeof 3.14                   // Returns number
typeof NaN                    // Returns number
typeof false                  // Returns boolean
typeof [1, 2, 3, 4]           // Returns object
typeof {name:'Bill', age:19}  // Returns object
typeof new Date()             // Returns object
typeof function () {}         // Returns function
typeof myCar                  // Returns undefined (if myCar is not declared)
typeof null                   // Returns object

Try It Yourself

Please note:

  • 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

You cannot use typeof to define if a JavaScript object is an array (or a date).

You cannot use typeof to determine if a JavaScript object is an array (or a date).

delete operator

delete The operator deletes properties from an object:

Example

var person = {firstName:"Bill", lastName:"Gates", age:19, eyeColor:"blue"};
delete person.age;   // Equivalent to delete person["age"];

Try It Yourself

The delete operator removes both the value and the property itself.

The property cannot be used until it is added back after deletion.

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

Note:Do not use the delete operator on predefined JavaScript object properties. This may cause your application to crash.

in operator

if the specified property exists in the specified object, then in The operator will return true, otherwise return false:

Example

// Arrays
var cars = ["Saab", "Volvo", "BMW"];
"Saab" in cars          // Returns false (specifies an index number rather than a 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:"Bill", lastName:"Gates", age:19};
"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

Try It Yourself

instanceof operator

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

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

Try It Yourself

void operator

void operator evaluates an expression and returns undefined. This operator is typically used to obtain the undefined original value using "void(0)" (very useful when evaluating an expression without using the returned 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>

Try It Yourself