Foundations Updated 2026-09 View as Markdown

Operators

The arithmetic, comparison and logical operators, and the two TypeScript-relevant ones: ?? and ?.

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<=x<1

And many more mathematical functions.

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

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