JavaScript operators

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Examples:

var x = 5;         // assign the value 5 to x
var y = 2;         // assign the value 2 to y
var z = x + y;     // assign the value 7 to z (x + y)

The assignment operator (=) assigns a value to a variable.

var x = 10;

var x = 5;
var y = 2;
var z = x + y; // Result 7

The multiplication operator (*) multiplies numbers.

var x = 5;
var y = 2;
var z = x * y; // Result 10

JavaScript Arithmetic Operators

Arithmetic operators are used to perform arithmetic on numbers:

Operator Description
- Subtraction
* Multiplication
** Exponentiation (ES6)
/ Division
% Modulus (Division Remainder)
++ Increment
-- Decrement

Note: Arithmetic operators are fully described in the JS Arithmetic chapter.

JavaScript Assignment Operators

Assignment operators assign values to JavaScript variables.

Operator Example Same As
= x = y x = y
+= x += y x = x + y
-= x -= y x = x - y
*= x *= y x = x * y
/= x /= y x = x / y
%= x %= y x = x % y

The addition assignment operator (+=) adds a value to a variable.

var x = 10;
x += 5; // Result 15

Note: Assignment operators are fully described in the JS Assignment chapter.

JavaScript String Operators

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

var txt1 = "John";
var txt2 = "Doe";
var txt3 = txt1 + " " + txt2;      // Result "John Doe"

The += assignment operator can also be used to add (concatenate) strings:

var txt1 = "What a very ";
txt1 += "nice day";      // Result "What a very nice day"

Note: When used on strings, the + operator is called the concatenation operator.

Adding Strings and Numbers

Adding two numbers, will return the sum, but adding a number and a string will return a string:

var x = 5 + 5;           // Result 10
var y = "5" + 5;         // Result 55
var z = "Hello" + 5;     // Result Hello5

Remember: If you add a number and a string, the result will be a string!

JavaScript Comparison Operators

Operator Description
== equal to
=== equal value and equal type
!= not equal
!== not equal value or not equal type
> greater than
< less than
>= greater than or equal to
<= less than or equal to
? ternary operator

Note: Comparison operators are fully described in the JS Comparisons chapter.

JavaScript Logical Operators

Operator Description
&& logical and
|| logical or
! logical not

Note: Logical operators are fully described in the JS Comparisons chapter.

JavaScript Type Operators

Operator Description
typeof Returns the type of a variable
instanceof Returns true if an object is an instance of an object type

Note: Type operators are fully described in the JS Type Conversion chapter.

Exercises - test your knowledge

Exercise 1

Multiply 10 with 5, and alert the result:

Exercise 2

Divide 10 by 2, and alert the result:

Exercise 3

x = 10

y = 5

Use the correct assignment operator that will result in x being 15 (same as x = x + y ).

x = 10;
y = 5;
x  += y;

Exercise 4

x = 10

y = 5

Use the correct assignment operator that will result in x being 50 (same as x = x * y ).

x = 10;
y = 5;
x *= y;

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