Javascript Operators Tutorial

In this Javascript tutorial we learn about operators. Symbols that have a special meaning to the translator and are able to perform various operations on our code.

We cover operands, lvalues and rvalues. We also cover arithmetic, assignment, relational (comparison), logical, incremental and decremental operators.

Lastly we briefly take a look at the ternary conditional operator ( ? : ) and the typeof operator.

Here's a table of contents of what you'll learn in this lesson:
(click on a link to skip to its section)

Let's jump right in.

What is an operator

An operator is one or more symbols that have a special meaning, in certain contexts, to the Javascript translator.

For example, the + symbol is the addition operator and will perform addition arithmetic on two numeric values.

The following types of operators are available in Javascript.

  • Arithmetic operators
  • Assignment operators
  • Relational (Comparison) operators
  • Logical operators
  • Ternary conditional operator
  • Other operators

You don’t need to memorize the following operators, we will cover most of them throughout the course. It’s sufficient to only know what they’re for, for the moment.

Operands, Lvalues & Rvalues

There are two kinds of expressions in Javascript, Lvalues and Rvalues. Lvalues and Rvalues are also known as the left operand and the right operand respectively, or operands in general.

An lvalue is the operand that can have a value assigned to it. It’s allowed to appear on either the left or the right side of an assignment.

Example:
// lvalue (num1) may be
// on the left of the =
var num1 = 10;

// lvalue may also be on
// the right of the =
var num2 = num1;

An rvalue is the operand that cannot be assigned a value. It may only appear on the right side of an assignment.

Example:
// rvalue (10) may only
// be on the right of the =
var num1 = 10;

// an rvalue cannot be
// on the left of the =
10 = 10

Arithmetic operators

Arithmetic operators allow basic mathematical arithmetic to be performed on operands.

The following table lists the arithmetic operators available in Javascript.

OperatorDescription
+Add the right operand to the left operand.
*Multiply the left operand with the right operand.
/Divide the left operand by the right operand.
%Modulo. Divide the left operand by the right operand and return the remainder of the division.

Assignment operators

An assignment operator is used to assign the operand on the right, to the operand on the left.

The following table lists the assignment operators available in Javascript.

OperatorDescriptionExampleSame as
=Assigna = ba = b
+=Add and assigna += ba = a+b
-=Subtract and assigna -= ba = a-b
*=Multiply and assigna *= ba = a* b
/=Divide and assigna /= ba = a/b
%=Modulo and assigna %= ba = a%b

Relational (comparison) operators

Relational operators evaluate the relationship between operands and are primarily used in conditional and iteration control flow.

The following table lists the relational operators available in Javascript.

OperatorDescriptionExample
==Equal to1 == 1 is true
===Equal to value and type"one" === 1 is false
>Greater than2 > 1 is true
<Less than3 < 1 is false
!=Not equal to2 != 3 is true
!===Not equal to value and type"two" !== 2 is true
>=Greater than or equal to2 >= 1 is true
<=Less than or equal to5 <= 5 is true

Logical operators

Logical operators are used to combine conditional evaluations. The result is either true or false.

The following table lists the logical operators available in Javascript.

OperatorNameDescription
&&AndReturns true if both expressions evaluate to true.
||OrReturns true if one or the other expression evaluate to true.
!NotReturns true if the expression immediately following it not true.

Increment (unary) operators

Incremental operators are used to increase a value incrementally, and decremental operators are used to decrease a value. These operators are what is known as unary operators and as such only require one operand.

The following table lists incremental and decremental operators available in Javascript.

OperatorNameDescription
++aPre-incrementIncrement by one, then return a.
a++Post-incrementReturn a, then increment by one.
--aPre-decrementDecrement by one, then return a.
a--Post-decrementReturn a, then decrement by one.

TypeOf (unary) operator

The typeof operator is another unary operator that evaluates if a value is of a certain data type. The typeof operator is placed before an operand and the result will be a string indicating the type.

Here is a list of the return values for the typeof operator in Javascript.

TypeString returned
Number"number"
String"string"
Boolean"boolean"
Object"object"
Function"function"
Undefined"undefined"
Null"object"
Example:
<script>

  var br = "<br>";

  var num = 10;
  var str = "Hello World";
  var auth = true;

  document.write("num = ", typeof num);
  document.write(br);
  document.write("str = ", typeof str);
  document.write(br);
  document.write("auth = ", typeof auth);

</script>

Ternary conditional operator ? :

The ternary operator is a conditional operator that functions as a replacement for a conditional if/else expression with only single execution statements.

OperatorDescription
? :Replaces a simple conditional if/else statement.
Example:
var num = 10;

if (num > 5) {

  document.write(num, " > 5");
} else {

  document.write(num, " < 5");
}

The normal if/else statement in the example above, will become the following expression when converted to a ternary.

Example:
var num = 10;

num > 5 ? document.write(num, " > 5") : document.write(num, " < 5");

We look at the ternary operator again in the lesson on conditional control with if/else statements.

Summary: Points to remember

  • There are two types of expressions in Javascript, lvalues and rvalues.
  • An lvalue may be placed on both sides of the assignment operator.
  • An rvalue may only be placed on the right side of the assignment operator.