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JavaScript Operators Reference

JavaScript Operators

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

There are different types of JavaScript operators:

  • Arithmetic Operators
  • Assignment Operators
  • Comparison Operators
  • Logical Operators
  • Conditional Operators
  • Type Operators

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:

Oper Name Example Results 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 »
** Exponentiation
ES2016
x=y**2 y=5, x=25 Try it »
/ Division x = y / 2 y=5, x=2.5 Try it »
% Remainder x = y % 2 y=5, x=1 Try it »
++ Pre increment x = ++y y=6, x=6 Try it »
++ Post increment x = y++ y=6, x=5 Try it »
-- Pre decrement x = --y y=4, x=4 Try it »
-- Post decrement x = y-- y=4, x=5 Try it »

For a tutorial about arithmetic operators, read our 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:

Oper Example Same As Result 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 »
: x: 45 size.x = 45 x = 45 Try it »

For a tutorial about assignment operators, read our JavaScript Assignment Tutorial.



JavaScript String Operators

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

Given that t1 = "Good ", t2 = "Morning", and t3 = "", the table below explains the operators:

Oper Example t1 t2 t3 Try it
+ t3 = t1 + t2 "Good " "Morning"  "Good Morning" Try it »
+= t1 += t2 "Good Morning" "Morning" Try it »

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:

Oper Name Comparing Returns Try it
== equal to x == 8 false Try it »
== equal to x == 5 true Try it »
=== equal value and type x === "5" false Try it »
=== equal value and type x === 5 true Try it »
!= not equal x != 8 true Try it »
!== not equal value or type x !== "5" true Try it »
!== not equal value or type x !== 5 false Try it »
> greater than x > 8 false Try it »
< less than x < 8 true Try it »
>= greater or equal to x >= 8 false Try it »
<= less or equal to x <= 8 true Try it »

For a tutorial about comparison operators, read our JavaScript Comparisons Tutorial.


Conditional (Ternary) Operator

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

Syntax Example Try it
(condition) ? x : y (z < 18) ? x : y Try it »

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:

Oper Name 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 »

The Nullish Coalescing Operator (??)

The ?? operator returns the first argument if it is not nullish (null or undefined).

Otherwise it returns the second argument.

Example

let name = null;
let text = "missing";
let result = name ?? text;
Try it Yourself »

The nullish operator is supported in all browsers since March 2020:

Chrome 80 Edge 80 Firefox 72 Safari 13.1 Opera 67
Feb 2020 Feb 2020 Jan 2020 Mar 2020 Mar 2020

The Optional Chaining Operator (?.)

The ?. operator returns undefined if an object is undefined or null (instead of throwing an error).

Example

// Create an object:
const car = {type:"Fiat", model:"500", color:"white"};
// Ask for car name:
document.getElementById("demo").innerHTML = car?.name;
Try it Yourself »

The optional chaining operator is supported in all browsers since March 2020:

Chrome 80 Edge 80 Firefox 72 Safari 13.1 Opera 67
Feb 2020 Feb 2020 Jan 2020 Mar 2020 Mar 2020

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.

Oper Name Example Same as Result Decimal Try it
& AND x = 5 & 1 0101 & 0001 0001 1 Try it »
| OR x = 5 | 1 0101 | 0001 0101 5 Try it »
~ NOT x = ~ 5 ~0101 1010 10 Try it »
^ XOR x = 5 ^ 1 0101 ^ 0001 0100 4 Try it »
<< Left shift x = 5 << 1 0101 << 1 1010 10 Try it »
>> Right shift x = 5 >> 1 0101 >> 1 0010 2 Try it »
>>> Unsigned right x = 5 >>> 1 0101 >>> 1 0010 2 Try it »

Note

The table above uses 4 bits unsigned number. Since JavaScript uses 32-bit signed numbers, ~ 5 will not return 10. It will return -6.

~00000000000000000000000000000101 (~5)
will return
11111111111111111111111111111010 (-6)


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
Try it Yourself »

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

Example

typeof "John"
typeof 3.14
typeof NaN
typeof false
typeof [1, 2, 3, 4]
typeof {name:'John', age:34}
typeof new Date()
typeof function () {}
typeof myCar
typeof null
Try it Yourself »

Note

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

Both array and date return object as type.


The delete Operator

The delete operator deletes a property from an object:

Example

const person = {
  firstName:"John",
  lastName:"Doe",
  age:50,
  eyeColor:"blue"
};
delete person.age;
Try it Yourself »

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 the properties of any predefined JavaScript objects (Array, Boolean, Date, Function, Math, Number, RegExp, and String).

This can crash your application.


The Spread (...) Operator

The ... operator expands an iterable into more elements (or more arguments for function calls):

Example

const cars1 = ["Saab", "Volvo", ..."BMW"];
const cars2 = ["Fiat", "Toyota"];

const combined = [cars1, ...cars2];
Try it Yourself »

The ... operator can be used to expand an iterable into more arguments for function calls:

Example

const numbers = [23,55,21,87,56];
let maxValue = Math.max(...numbers);
Try it Yourself »

The in Operator

The in operator returns true if a property is in an object, otherwise false:

Obect Example

const person = {firstName:"John", lastName:"Doe", age:50};
("firstName" in person);
("age" in person);
Try it Yourself »

Note

You cannot use in to check for array content like ("Volvo" in cars).

Array properties can only be index (0,1,2,3...) and length.

See the examples below.

Examples

const cars = ["Saab", "Volvo", "BMW"];
("Saab" in cars);
Try it Yourself »
const cars = ["Saab", "Volvo", "BMW"];
(0 in cars);
(1 in cars);
(4 in cars);
("length" in cars);
Try it Yourself »

Predefined Objects

("PI" in Math);
("NaN" in Number);
("length" in String);
Try it Yourself »

The instanceof Operator

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

Example

const 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 »

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>
Try it Yourself »