An expression is a special kind of statement that evaluates to a value. Every expression is composed of −

• Operands − Represents the data.

• Operator − Defines how the operands will be processed to produce a value.

Consider the following expression- 2 + 3. Here in the expression, 2 and 3 are operands and the symbol + (plus) is the operator. JavaScript supports the following types of operators −

• Arithmetic operators
• Logical operators
• Relational operators
• Bitwise operators
• Assignment operators
• Ternary/conditional operators
• String operators
• Type operators
• The void operator

Arithmetic Operators

Assume the values in variables a and b are 10 and 5 respectively.

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Relational Operators

Relational operators test or define the kind of relationship between two entities. Relational operators return a boolean value, i.e. true/false.

Assume the value of A is 10 and B is 20.

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Logical Operators

Logical operators are used to combine two or more conditions. Logical operators, too, return a Boolean value. Assume the value of variable A is 10 and B is 20.

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Bitwise Operators

JavaScript supports the following bitwise operators. The following table summarizes JavaScript”s bitwise operators.

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Assignment Operators

The following table summarizes Assignment operators.

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Note − The same logic applies to Bitwise operators, so they will become <<=, >>=, >>=, &=, |= and ^=.

Miscellaneous Operators

Following are some of the miscellaneous operators.

The negation operator (-)

Changes the sign of a value. The following program is an example of the same.

var x = 4 
var y = -x; 
console.log("value of x: ",x); //outputs 4 
console.log("value of y: ",y); //outputs -4

The following output is displayed on successful execution of the above program.

value of x: 4 
value of y: -4 

String Operators : Concatenation operator (+)

The + operator when applied to strings appends the second string to the first. The following program helps to understand this concept.

var msg = "hello"+"world" 
console.log(msg) 

The following output is displayed on successful execution of the above program.

helloworld

The concatenation operation doesn’t add a space between the strings. Multiple strings can be concatenated in a single statement.

Conditional Operator (?)

This operator is used to represent a conditional expression. The conditional operator is also sometimes referred to as the ternary operator. Following is the syntax.

Test ? expr1 : expr2

Where,

Test − Refers to the conditional expression

expr1 − Value returned if the condition is true

expr2 − Value returned if the condition is false

Example

var num = -2 
var result = num > 0 ?"positive":"non-positive" 
console.log(result)

Line 2 checks whether the value in the variable num is greater than zero. If num is set to a value greater than zero, it returns the string “positive” else a “non-positive” string is returned.

The following output is displayed on successful execution of the above program.

non-positive 

typeof operator

It is a unary operator. This operator returns the data type of the operand. The following table lists the data types and the values returned by the typeof operator in JavaScript.

The following example code displays the number as the output.

var num = 12 
console.log(typeof num); //output: number

The following output is displayed on successful execution of the above code.

number

Spread Operator

ES6 provides a new operator called the spread operator. The spread operator is represented by three dots “…” . The spread operator converts an array into individual array elements.

Spread operator and function

The following example illustrates the use of spread operators in a function

<script>
   function addThreeNumbers(a,b,c){
      return a+b+c;
   }
   const arr = [10,20,30]
   console.log(''sum is :'',addThreeNumbers(...arr))
   console.log(''sum is '',addThreeNumbers(...[1,2,3]))
</script>

The output of the above code will be as seen below −

sum is : 60
sum is 6

Spread operator and Array copy and concat

The spread operator can be used to copy one array into another. It can also be used to concatenate two or more arrays. This is shown in the example below −

Example

<script>
   //copy array using spread operator
   let source_arr = [10,20,30]
   let dest_arr = [...source_arr]
   console.log(dest_arr)
	
   //concatenate two arrays
   let arr1 = [10,20,30]
   let arr2 =[40,50,60]
   let arr3 = [...arr1,...arr2]
   console.log(arr3)
</script>

The output of the above code will be as stated below −

[10, 20, 30]
[10, 20, 30, 40, 50, 60]

Spread Operator and Object copy and concatenation

The spread operator can be used to copy one object into another. It can also be used to concatenate two or more objects. This is shown in the example below −

<script>
   //copy object
   let student1 ={firstName:''Mohtashim'',company:''TutorialsPoint''}
   let student2 ={...student1}
   console.log(student2)
   //concatenate objects
   let student3 = {lastName:''Mohammad''}
   let student4 = {...student1,...student3}
   console.log(student4)
</script>

The output of the above code will be as given below −

{firstName: "Mohtashim", company: "TutorialsPoint"}
{firstName: "Mohtashim", company: "TutorialsPoint", lastName: "Mohammad"}