Foundations Updated 2026-09 View as Markdown

Operators

Every variable in JavaScript is casted automatically so any operator between two variables will always give some kind of result.

Every variable in JavaScript is casted automatically so any operator between two variables will always give some kind of result.

The addition operator#

The + (addition) operator is used for both addition and concatenation of strings.

For example, adding two variables is easy:

let a = 1;
let b = 2;
let c = a + b;     // c is now equal to 3

The addition operator is used for concatenating strings to strings, strings to numbers, and numbers to strings:

let name = "John";
console.log("Hello " + name + "!");
console.log("The meaning of life is " + 42);
console.log(42 + " is the meaning of life");

JavaScript behaves differently when you are trying to combine two operands of different types. The default primitive value is a string, so when you try to add a number to a string, JavaScript will transform the number to a string before the concatenation.

console.log(1 + "1");   // outputs "11"

Mathematical operators#

To subtract, multiply and divide two numbers, use the minus (-), asterisk (*) and slash (/) signs.

console.log(3 - 5);     // outputs -2
console.log(3 * 5);     // outputs 15
console.log(3 / 5);     // outputs 0.6

Advanced mathematical operators#

JavaScript supports the modulus operator (%) which calculates the remainder of a division operation.

console.log(5 % 3);     // outputs 2

JavaScript also supports combined assignment and operation operators. So, instead of typing myNumber = myNumber / 2, you can type myNumber /= 2. Here is a list of all these operators:

• /=

• *=

• -=

• +=

• %=

JavaScript also has a Math module which contains more advanced functions:

• Math.abs calculates the absolute value of a number

• Math.exp calculates e to the power of a number

• Math.pow(x,y) calculates the result of x to the power of y

• Math.floor removes the fraction part from a number

• Math.random() will give a random number x where 0

The name is John Smith
The meaning of life is 42

let firstName = "John";
let lastName = "Smith";
let myNumber = 21;

// TODO: change the following code
let fullName = firstName + " " + lastName;
let meaningOfLife = myNumber \* 2;

console.log("The name is " + fullName);
console.log("The meaning of life is " + meaningOfLife);