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JavaScript has only one type of number. Numbers can be written with or without decimals.
let a = 10.76; // A number with decimals
let b = 10; // A number without decimals
Extra large or extra small numbers can be written with scientific (exponent) notation
let a = 123e5; // 12300000
let b = 123e-5; // 0.00123
Unlike many other programming languages, JavaScript does not define different types of numbers, like integers, short, long, floating-point etc.
JavaScript numbers are always stored as double precision floating point numbers, following the international IEEE 754 standard.
This format stores numbers in 64 bits, where the number (the fraction) is stored in bits 0 to 51, the exponent in bits 52 to 62, and the sign in bit 63.
| Value (aka Fraction/Mantissa) | Exponent | Sign |
|---|---|---|
| 52 bits (0 - 51) | 11 bits (52 - 62) | 1 bit (63) |
Integers (numbers without a period or exponent notation) are accurate up to 15 digits. The maximum number of decimals is 17.
let a = 999999999999999; // x will be 999999999999999
let b = 9999999999999999; // y will be 10000000000000000
Floating point arithmetic is not always 100% accurate:
let a = 0.2 + 0.1; // a = 0.30000000000000004
// To solve the problem above, it helps to multiply and divide:
let a = (0.2 * 10 + 0.1 * 10) / 10; // a = 0.3
JavaScript uses the + operator for both addition and concatenation. Numbers are added. Strings are concatenated.
If you add two numbers, the result will be a number.
If you add two strings, the result will be a string concatenation.
If you add a number and a string, the result will be a string concatenation
let a = 10;
let b = 20;
let c = a + b; // c = 30
let k = "10";
let l = "20";
let m = k + l; // m = 1020
let x = a + l; // m = 1020
// Misleading Behavior
let y = "The output of a + b: " + a + b; // y = The output of a + b: 1020
let z = a + b + k; // m = The output of a + b: 3010
JavaScript will try to convert strings to numbers in all numeric operations except addition (concatenation).
let a = "100";
let b = "10";
// Divide
let c = a / b; // c = 10
// Multiply
let c = a * b; // c = 1000
// Subtraction
let c = a - b; // c = 90
// Subtraction
let c = a + b; // c = 10010
NaN is a JavaScript reserved word indicating that a number is not a legal number. Trying to do arithmetic with a non-numeric string will result in NaN (Not a Number).
You can use the global JavaScript function isNaN() to find out if a value is a not a number.
let a = 100 / "Apple"; // a = NaN
isNaN(a); // returns false
typeof NaN; // returns numbers
Infinity (or -Infinity) is the value JavaScript will return if you calculate a number outside the largest possible number.
let myNumber = 2;
// Execute until Infinity
while (myNumber != Infinity) {
myNumber = myNumber * myNumber;
}
let x = 2 / 0; // returns Infinity
let y = -2 / 0; // returns -Infinity
typeof Infinity; // returns number
Normally JavaScript numbers are primitive values created from literals. But numbers can also be defined as objects with the keyword new.
let a = new Number(123);
let a = 100;
let b = new Number(100);
let c = new Number(100);
(a == b) // returns true
(a === b) // returns false
(b == c) // returns false
(b === c) // returns false
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