JavaScript Numbers
JavaScript Numbers
JavaScript has only one type of number. Numbers can be written with or without decimals.
var x = 3.14; // A number with decimals
var y = 3; // A number without decimals
Extra large or extra small numbers can be written with scientific (exponent) notation:
var x = 123e5; // 12300000
var y = 123e-5; // 0.00123
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:
Precision
Integers (numbers without a period or exponent notation) are accurate up to 15 digits.
var x = 999999999999999; // x will be 999999999999999
var y = 9999999999999999; // y will be 10000000000000000
The maximum number of decimals is 17, but floating point arithmetic is not always 100% accurate:
var x = 0.2 + 0.1; // x will be 0.30000000000000004
To solve the problem above, it helps to multiply and divide:
var x = (0.2 * 10 + 0.1 * 10) / 10; // x will be 0.3
Adding Numbers and Strings
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:
var x = 10;
var y = 20;
var z = x + y; // z will be 30 (a number)
If you add two strings, the result will be a string concatenation:
var x = "10";
var y = "20";
var z = x + y; // z will be 1020 (a string)
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.
var x = 10;
var y = 20;
var z = "30";
var result = x + y + z;
Numeric Strings
JavaScript strings can have numeric content.
JavaScript will try to convert strings to numbers in all numeric operations:
var x = "100";
var y = "10";
var z = x / y; // z will be 10
var x = "100";
var y = "10";
var z = x * y; // z will be 1000
var x = "100";
var y = "10";
var z = x - y; // z will be 90
But this will not work. JavaScript uses the + operator to concatenate the strings.
var x = "100";
var y = "10";
var z = x + y; // z will not be 110 (It will be 10010)
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):
var x = 100 / "Apple"; // x will be NaN (Not a Number)
However, if the string contains a numeric value , the result will be a number:
var x = 100 / "10"; // x will be 10
You can use the global JavaScript function isNaN() to find out if a value is a number:
var x = 100 / "Apple";
isNaN(x); // returns true because x is Not a Number
NaN is a number: typeof NaN returns number:
typeof NaN; // returns "number"
var x = NaN;
var y = "5";
var z = x + y; // z will be NaN5
Infinity
Infinity (or -Infinity) is the value JavaScript will return if you calculate a number outside the largest possible number.
var myNumber = 2;
while (myNumber != Infinity) { // Execute until Infinity
myNumber = myNumber * myNumber;
}
Division by 0 (zero) also generates Infinity:
var x = 2 / 0; // x will be Infinity
var y = -2 / 0; // y will be -Infinity
Hexadecimal
JavaScript interprets numeric constants as hexadecimal if they are preceded by 0x.
var x = 0xFF; // x will be 255
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.
var 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
Numbers Can be Objects
Normally JavaScript numbers are primitive values created from literals:.
var x = 123;
But numbers can also be defined as objects with the keyword new: var y = new Number(123);
var x = 123;
var y = new Number(123);
// typeof x returns number
// typeof y returns object
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:
var x = 500;
var y = new Number(500);
// (x == y) is true because x and y have equal values
When using the === operator, equal numbers are not equal, because the === operator expects equality in both type and value.
var x = 500;
var y = new Number(500);
// (x === y) is false because x and y have different types
Or even worse. Objects cannot be compared. The difference between (x==y) and (x===y). Comparing two JavaScript objects will always return false.
var x = new Number(500);
var y = new Number(500);
// (x == y) is false because objects cannot be compared
