JavaScript Arithmetic Operators

Summary: in this tutorial, you will learn how to use JavaScript arithmetic operators to perform arithmetic calculations.

Introduction to the JavaScript Arithmetic Operators

JavaScript supports the following standard arithmetic operators:

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); // 30Code language: JavaScript (javascript)

You can also use the addition operator with two variables. For example:

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

console.log(grossPrice);Code language: JavaScript (javascript)

Output:

11.98Code language: CSS (css)

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 concatenate two strings:

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

console.log(result);Code language: JavaScript (javascript)

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);    Code language: JavaScript (javascript)

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:

Subtraction operator (-)

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

let result = 30 - 10;
console.log(result); // 20Code language: JavaScript (javascript)

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:

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);Code language: JavaScript (javascript)

Output:

6

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

let result = '5' * 2;

console.log(result);Code language: JavaScript (javascript)

Output:

10

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

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); // 2Code language: JavaScript (javascript)

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;Code language: JavaScript (javascript)

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

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);
Code language: JavaScript (javascript)

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);
Code language: JavaScript (javascript)

Output:

40
150
25
75

More on the valueOf vs. toString methods of the object.

Summary

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

Quiz