Introduction to the JavaScript Arithmetic Operators

JavaScript supports the following standard arithmetic operators:

Operator	Sign
Addition	+
Subtraction	–
Multiplication	*
Division	/

An arithmetic operator accepts numerical values as operands and returns a single numerical value. The numerical values can be literals or variables.

Addition operator (+)

The addition operator returns the sum of two values. For example, the following uses the addition operator to calculate the sum of two numbers:

let sum = 10 + 20;
console.log(sum);// 30

Also, you can use the addition operator with two variables. For example:

let netPrice    = 9.99,
    shippingFee = 1.99;
let grossPrice  = netPrice + shippingFee;

console.log(grossPrice);

Output:

11.98

If either value is a string, the addition operator uses the following rules:

• If both values are strings, it concatenates the second string to the first one.
• If one value is a string, it implicitly converts the numeric value into a string and concatenates two strings.

For example, the following uses the addition operator to add concatenate two strings:

let x = '10',
    y = '20';
let result = x + y;

console.log(result);

Output:

1020

The following example shows how to use the addition operator to calculate the sum of a number and a string:

let result = 10 + '20';

console.log(result);

Output:

1020

In this example, JavaScript converts the number 10 into a string '10' and concatenates the second string '20' to it.

The following table shows the result when using the addition operator with special numbers:

First Value	Second Value	Result	Explanation
NaN		NaN	If either value is NaN, the result is NaN
Infinity	Infinity	Infinity	Infinity + Infinity = Infinity
-Infinity	-Infinity	-Infinity	-Infinity + ( -Infinity) = – Infinity
Infinity	-Infinity	NaN	Infinity + -Infinity = NaN
+0	+0	+0	+0 + (+0) = +0
-0	+0	+0	-0 + (+0) = +0
-0	-0	-0	-0 + (-0) = -0

Subtraction operator (-)

The subtraction operator (-) subtracts one number from another. For example:

let result = 30 - 10;
console.log(result);// 20

If a value is a string, a boolean, null, or undefined, the JavaScript engine will:

• First, convert the value to a number using the Number() function.
• Second, perform the subtraction.

The following table shows how to use the subtraction operator with special values:

First Value	Second Value	Result	Explanation
NaN		NaN	If either value is NaN, the result is NaN
Infinity	Infinity	NaN	Infinity – Infinity = NaN
-Infinity	-Infinity	-Infinity	-Infinity – ( -Infinity) = NaN
Infinity	-Infinity	Infinity	Infinity
+0	+0	+0	+0 – (+0) = 0
+0	-0	-0	+0 – (-0) = 0
-0	-0	+0	-0 – (-0) = 0

Multiplication operator (*)

JavaScript uses the asterisk (*) to represent the multiplication operator. The multiplication operator multiplies two numbers and returns a single value. For example:

let result = 2 * 3;
console.log(result);

Output:

6

If either value is not a number, the JavaScript engine implicitly converts it into a number using the Number() function and performs the multiplication. For example:

let result = '5' * 2;

console.log(result);

Output:

10

The following table shows how the multiply operator behaves with special values:

First Value	Second Value	Result	Explanation
NaN		NaN	If either value is NaN, the result is NaN
Infinity	0	NaN	Infinity * 0 = NaN
Infinity	Positive number	Infinity	-Infinity * 100 = -Infinity
Infinity	Negative number	-Infinity	Infinity * (-100) = -Infinity
Infinity	Infinity	Infinity	Infinity * Infinity = Infinity

Divide operator (/)

Javascript uses the slash (/) character to represent the divide operator. The divide operator divides the first value by the second one. For example:

let result = 20 / 10;

console.log(result);// 2

If either value is not a number, the JavaScript engine converts it into a number for division. For example:

let result = '20' / 2;
console.log(result);// 10;

The following table shows the divide operators’ behavior when applying to special values:

First Value	Second Value	Result	Explanation
NaN		NaN	If either value is NaN, the result is NaN
A number	0	Infinity	1/0 = Infinity
Infinity	Infinity	NaN	Infinity / Infinity = NaN
0	0	NaN	0/0 = NaN
Infinity	A positive number	Infinity	Infinity / 2 = Infinity
Infinity	A negative number	-Infinity	Infinity / -2 = -Infinity

Using JavaScript arithmetic operators with objects

If a value is an object, the JavaScript engine will call the valueOf() method of the object to get the value for calculation. For example:

let energy = {
  valueOf() {
    return 100;
  },
};

let currentEnergy = energy - 10;
console.log(currentEnergy);

currentEnergy = energy + 100;
console.log(currentEnergy);

currentEnergy = energy / 2;
console.log(currentEnergy);

currentEnergy = energy * 1.5;
console.log(currentEnergy);

Output:

90
200
50
150

If the object doesn’t have the valueOf() method but has the toString() method, the JavaScript engine will call the toString() method to get the value for calculation. For example:

let energy = {
  toString() {
    return 50;
  },
};

let currentEnergy = energy - 10;
console.log(currentEnergy);

currentEnergy = energy + 100;
console.log(currentEnergy);

currentEnergy = energy / 2;
console.log(currentEnergy);

currentEnergy = energy * 1.5;
console.log(currentEnergy);

Output:

40
150
25
75

Summary

• Use the JavaScript arithmetic operators including addition (+), subtraction (), multiply (), and divide (/) to perform arithmetic operations.