JavaScript Numbers
JavaScript has only one type of number. Numbers can be written with or without decimals.
Example
let x = 3.14; // A number with decimals
let y = 3; // A number without decimals
Extra large or extra small numbers can be written with scientific (exponent) notation:
JavaScript Numbers are Always 64-bit Floating Point
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) |
Precision
Integers (numbers without a period or exponent notation) are accurate up to 15 digits.
Example
let x = 999999999999999; // x will be 999999999999999
let y = 9999999999999999; // y will be 10000000000000000
Try it Yourself »
The maximum number of decimals is 17, but floating point arithmetic is not always 100% accurate:
To solve the problem above, it helps to multiply and divide:
Adding Numbers and Strings
WARNING !!
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:
If you add a string and a number, the result will be a string concatenation:
A common mistake is to expect this result to be 30:
A common mistake is to expect this result to be 102030:
The JavaScript interpreter works from left to right.
First 10 + 20 is added because x and y are both numbers.
Then 30 + "30" is concatenated because z is a string.
Numeric Strings
JavaScript strings can have numeric content:
let x = 100; // x is a number
let y = "100"; // y is a
string
JavaScript will try to convert strings to numbers in all numeric operations:
This will work:
let x = "100";
let y = "10";
let z = x / y; // z will be 10
This will also work:
let x = "100";
let y = "10";
let z = x * y; // z will be 1000
And this will work:
let x = "100";
let y = "10";
let z = x - y; // z will be 90
But this will not work:
let x = "100";
let y = "10";
let z = x + y; // z will not be 110 (It will be 10010)
In the last example JavaScript uses the + operator to concatenate the strings.
NaN - Not a Number
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):
However, if the string contains a numeric value , the result will be a number:
You can use the global JavaScript function isNaN() to find out if a value is a number:
Watch out for NaN. If you use NaN in a mathematical operation, the result will also be NaN:
Or the result might be a concatenation:
NaN is a number: typeof NaN returns number:
Infinity
Infinity (or -Infinity) is the value JavaScript will return if you calculate a number outside the largest
possible number.
Example
let myNumber = 2;
while (myNumber != Infinity) { // Execute until Infinity
myNumber = myNumber * myNumber;
}
Try
it yourself »Division by 0 (zero) also generates Infinity:
Example
let x = 2 / 0;
// x will be Infinity
let y = -2 / 0; // y will be -Infinity
Try it Yourself »
Infinity is a number: typeof Infinity returns number.
Hexadecimal
JavaScript interprets numeric constants as hexadecimal if they are preceded by 0x.
Never write a number with a leading zero (like 07).
Some JavaScript versions interpret
numbers as octal if they are written with a leading zero.
By default, JavaScript displays numbers as base 10 decimals.
But you can use the toString() method to output numbers from base 2
to base 36.
Hexadecimal is base 16. Decimal is base 10. Octal is base 8. Binary is base 2.
Example
let myNumber = 32;
myNumber.toString(10); // returns 32
myNumber.toString(32); // returns
10
myNumber.toString(16); // returns 20
myNumber.toString(8); // returns 40
myNumber.toString(2); // returns 100000
Try it Yourself »
Numbers Can be Objects
Normally JavaScript numbers are primitive values created from literals:
let x = 123;
But numbers can also be defined as objects with the keyword new:
let y = new
Number(123);
Example
let x = 123;
let y = new Number(123);
//
typeof x returns number
//
typeof y returns object
Try
it yourself »
Do not create Number objects.
It slows down execution speed.
The new keyword complicates
the code. This can produce some unexpected results:
When using the == operator, equal
numbers are equal:
Example
let x = 500;
let y = new Number(500);
// (x == y) is true because x and y have equal values
Try it Yourself »
When using the === operator, equal numbers are not equal, because the === operator expects equality in both type and value.
Example
let x = 500;
let y = new Number(500);
// (x === y) is false because x and y have different types
Try it Yourself »
Or even worse. Objects cannot be compared:
Example
let x = new Number(500);
let y = new Number(500);
// (x == y) is false because objects cannot be compared
Try it Yourself »
Note the difference between (x==y) and (x===y).
Comparing two JavaScript objects will always return false.
