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Numbers

What are numbers?​

Numbers are used to represent numeric values in JavaScript. JavaScript has one number type that handles both integers and floating-point numbers. Numbers are one of the primitive data types and are immutable.

const age = 30;
const price = 19.99;
const temperature = -5;

Number literals​

You can create numbers using numeric literals:

const integer = 42;
const decimal = 3.14;
const negative = -10;
const large = 1000000;
const scientific = 1e6;  // 1000000 (1 × 10^6)

Integer literals​

Integers are whole numbers without decimal points:

const count = 5;
const year = 2024;
const negative = -42;

Floating-point literals​

Floating-point numbers include a decimal point:

const pi = 3.14159;
const price = 19.99;
const small = 0.001;

Scientific notation​

For very large or very small numbers, you can use scientific notation:

const million = 1e6;      // 1000000
const billion = 1e9;      // 1000000000
const tiny = 1e-6;        // 0.000001
const verySmall = 2.5e-3; // 0.0025

Number operations​

Arithmetic operators​

JavaScript supports standard arithmetic operations:

const a = 10;
const b = 3;

a + b;  // 13 (addition)
a - b;  // 7 (subtraction)
a * b;  // 30 (multiplication)
a / b;  // 3.3333333333333335 (division)
a % b;  // 1 (modulo - remainder)
a ** b; // 1000 (exponentiation)

Order of operations​

JavaScript follows standard mathematical order of operations (PEMDAS):

const result = 2 + 3 * 4;     // 14 (not 20)
const result2 = (2 + 3) * 4;  // 20 (parentheses change order)

Increment and decrement​

let count = 5;

count++;  // 6 (increment by 1)
count--;  // 5 (decrement by 1)
count += 2; // 7 (add 2)
count -= 1; // 6 (subtract 1)
count *= 2; // 12 (multiply by 2)
count /= 3; // 4 (divide by 3)

Number methods​

Converting to strings​

const num = 42;

num.toString();      // "42"
num.toString(2);     // "101010" (binary)
num.toString(16);    // "2a" (hexadecimal)
String(num);         // "42" (alternative)

Rounding numbers​

const num = 3.7;

Math.round(num);     // 4 (rounds to nearest integer)
Math.floor(num);     // 3 (rounds down)
Math.ceil(num);      // 4 (rounds up)
Math.trunc(num);     // 3 (removes decimal part)

Formatting numbers​

const num = 1234.567;

num.toFixed(2);      // "1234.57" (2 decimal places)
num.toPrecision(5);  // "1234.6" (5 significant digits)
num.toLocaleString(); // "1,234.567" (locale-specific formatting)

Special number values​

Infinity​

const positiveInfinity = Infinity;
const negativeInfinity = -Infinity;
const result = 1 / 0;  // Infinity

NaN (Not a Number)​

NaN represents a value that is "not a number" (often from invalid operations):

const result = 0 / 0;        // NaN
const result2 = "text" / 2;  // NaN
const result3 = Math.sqrt(-1); // NaN

// Checking for NaN
isNaN(result);        // true
Number.isNaN(result); // true (more reliable)

Checking for finite numbers​

const num = 42;
const inf = Infinity;
const nan = NaN;

isFinite(num);  // true
isFinite(inf);  // false
isFinite(nan);  // false

Number conversion​

Converting strings to numbers​

const str = "42";

Number(str);        // 42
parseInt(str);      // 42 (parses integer)
parseInt("42.7");   // 42 (stops at decimal)
parseFloat("42.7"); // 42.7 (parses floating-point)
+"42";              // 42 (unary plus operator)

Converting other types to numbers​

Number(true);   // 1
Number(false);  // 0
Number(null);   // 0
Number(undefined); // NaN
Number("");     // 0
Number(" 42 "); // 42 (trims whitespace)
Number("abc");  // NaN

Common number patterns​

Checking if a value is a number​

const value = 42;

typeof value === "number";  // true
Number.isInteger(value);    // true (checks if integer)
Number.isFinite(value);     // true (checks if finite number)

Generating random numbers​

Math.random();                    // Random number between 0 and 1
Math.random() * 10;               // Random number between 0 and 10
Math.floor(Math.random() * 10);   // Random integer between 0 and 9
Math.floor(Math.random() * 10) + 1; // Random integer between 1 and 10

// Random number in a range
function randomInRange(min, max) {
  return Math.floor(Math.random() * (max - min + 1)) + min;
}
randomInRange(5, 10); // Random integer between 5 and 10

Finding min and max​

Math.min(5, 10, 2);  // 2
Math.max(5, 10, 2);  // 10

const numbers = [5, 10, 2, 8];
Math.min(...numbers); // 2
Math.max(...numbers); // 10

Absolute value​

Math.abs(-5);  // 5
Math.abs(5);   // 5

Power and square root​

Math.pow(2, 3);    // 8 (2 to the power of 3)
2 ** 3;            // 8 (exponentiation operator - preferred)
Math.sqrt(16);     // 4
Math.cbrt(8);      // 2 (cube root)

Number precision and limitations​

Floating-point precision​

JavaScript uses 64-bit floating-point numbers, which can lead to precision issues:

0.1 + 0.2;  // 0.30000000000000004 (not exactly 0.3)

For financial calculations, consider using libraries that handle decimal arithmetic, or work with integers (cents instead of dollars).

Safe integers​

JavaScript has a maximum safe integer:

Number.MAX_SAFE_INTEGER;  // 9007199254740991
Number.MIN_SAFE_INTEGER;  // -9007199254740991

Number.isSafeInteger(9007199254740991);  // true
Number.isSafeInteger(9007199254740992); // false

Common math methods​

Math.PI;           // 3.141592653589793
Math.E;            // 2.718281828459045
Math.sin(0);       // 0 (sine)
Math.cos(0);       // 1 (cosine)
Math.tan(0);       // 0 (tangent)
Math.log(10);      // 2.302585092994046 (natural logarithm)
Math.log10(100);   // 2 (base-10 logarithm)