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JavaScript Number Tutorial with Examples

  1. ECMAScript Number
  2. Compare numbers
  3. Constants
  4. Static methods
  5. Methods

1. ECMAScript Number

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In ECMAScript, the Number data type represents for a number, which can be an Integer, or a Floating-point Number.
Based on memory-based management way, Number is divided into the 2 kinds: Number Object and Number Primitive:
Number Primitive:
Normally, to create a number, you should use the Primitive syntax:
// Primitive Syntax:

var myNumber1 = 100;
var myNumber2 = 55.1;
Number primitives are managed in Common Pool, which means when you declare 2 or more Number primitives with the same value. They will point to the same memory location in the Common Pool.
The === operator is used to check if two variables point to the same address on memory or not.
number-primitive-example1.js
let a = 100;
let b = 150.1;
let c = 150.1;

// a, b: Same address?
console.log( a === b); // false

// b, c: Same address?
console.log( b === c); // true
You can also create a number by using the Number(value) function. The result received by you is a Number primitive:
number-primitive-example2.js
let a = 100;
let b = 150.1;

// Using Number() function
let c = Number(150.1);

// a, b: Same address?
console.log( a === b); // false

// b, c: Same address?
console.log( b === c); // true
Number object:
You can create a number through the constructor of Number class. In this case, you will receive a Number object.
// Syntax:

var aNumber = new Number(number);

// Example:
var myNumber1 = new Number(100);
var myNumber2 = new Number(150.1);
The new operator always creates a new entity on the Heap memory.
When you assign the new value which is variable aa to the variable bb . The variable bb will point to the address on memory to which the variable aa is pointing. No entity will be created on memory in this case.
number-object-example2.js
let aa = new Number(100);

let bb = aa;

// aa, bb: Same address?
var sameAddress = aa === bb;

console.log( sameAddress); // true
Number object vs Number primitive
Number primitives are stored on the Stack (Common Pool). While Number objects are created and stored on the Heap memory, it requires a complex memory management and wastes storage space. Therefore, you should use Number primitive instead of Number object as anytime as possible.
typeof
The typeof(Number_object) operator will return the 'object' string, while the typeof(Number_primitive) will return the 'number' string:
typeof-example.js
let myNumberObject = new Number(200);
console.log(myNumberObject); // [Number: 200]
console.log( typeof(myNumberObject) ); // object

let myNumberPrimitive =  500;
console.log(myNumberPrimitive); // 500
console.log( typeof(myNumberPrimitive) ); // number

2. Compare numbers

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The === operator is used to compare the addresses on memory to which two variables are pointing.
comparing-example.js
var a = new Number(100);
var b = new Number(100);

var c = 100; // Stored in Common Pool.
var d = 100; // Stored in Common Pool.

console.log( a === b); // false

console.log( c === d); // true

console.log( a === c); // false
The == operator is used to compare the values of two variables. It works perfectly for primitive data types such as Boolean (primitive), Number (primitive), String (Literal), null, undefined, NaN. But it may work not in the way you are thinking for Object data types. The Number data type in ECMAScript can be Primitive or Object, therefore, you need to be careful when using this operator.
Example: The == operator works perfectly when comparing Number Primitives:
comparing-example2.js
let a = 100;
let b = 100;
let c = 120;

console.log( a == b); // true
console.log( a == c); // false
Example: The == operator works not in the way you are think of which comparing 2 Number objects:
comparing-example3.js
let a = new Number(100);
let b = new Number(100);
let c = new Number(120);

// Are you expecting true value?
console.log( a == b); // false

console.log( a == c); // false
If you are not sure that your variable is Number object or Number primitive, you should use Number(value) function to convert it to Number primitive before using the == operator.
comparing-example3b.js
let a = new Number(100);
let b = new Number(100);
let c = new Number(120);

console.log( a == b); // false

// Use Number() function to convert Number-object to Number-literal
console.log( Number(a) == Number(b) ); // true

console.log( a == c); // false
Example: Use the == operator to compare the value of a Number primitive and the value of a Number object:
comparing-example4.js
let a = 100;
let b = new Number(100);

let c = new Number(120);

console.log( a == b); // true
console.log( a == c); // false

3. Constants

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The Number class predefines a few important Constants:
  • Number.EPSILON
  • Number.MAX_SAFE_INTEGER
  • Number.MAX_VALUE
  • Number.MIN_SAFE_INTEGER
  • Number.MIN_VALUE
  • Number.NEGATIVE_INFINITY
  • Number.NaN
  • Number.POSITIVE_INFINITY
Number.EPSILON
The smallest interval between two representable numbers.
epsilon-example.js
var interval = Number.EPSILON;

console.log(interval); // 2.220446049250313e-16
Number.MAX_SAFE_INTEGER
The largest integer that the ECMAScript can represent ( 2^53-1 ).
max-safe-integer-exampl
// 2^53 - 1
console.log( Number.MAX_SAFE_INTEGER); // 9007199254740991

console.log( Number.MAX_SAFE_INTEGER.toExponential() ); // 9.007199254740991e+15
Number.MIN_SAFE_INTEGER
The minimum interger that the ECMAScript can represent ( -(2^53-1) ).
min-safe-integer-example.js
// - (2^53 - 1)
console.log( Number.MIN_SAFE_INTEGER); // -9007199254740991

console.log( Number.MIN_SAFE_INTEGER.toExponential() ); // -9.007199254740991e+15
Number.MAX_VALUE
The maximum number can be represented by the ECMAScript .
max-value-example.js
console.log( Number.MAX_VALUE); // 1.7976931348623157e+308
Number.MIN_VALUE
The minimum number can be represented by the ECMAScript .
min-value-example.js
console.log( Number.MIN_VALUE); // 5e-324
Number.NaN
Specify the "Not a number" value.
Example:
If the value of the parameter passed to the constructor of the Number by you is not a number, you will get the NaN (Not-a-Number) object. Or in other situation, if you divide a string by a nuumber, the received value is also NaN.
NaN-example.js
let a = new Number("A String");
console.log(a); // [Number: NaN]
console.log( typeof a ); // object

let b = "A String" / 100;
console.log(b); // NaN
console.log( typeof b ); // number
Number.NEGATIVE_INFINITY
Value represents a Negative infinity.
negative-infinity-example.js
let a = -1 / 0;

console.log(a); // -Infinity

console.log( Number.NEGATIVE_INFINITY ); // -Infinity

console.log( a == Number.NEGATIVE_INFINITY); // true
Number.POSITIVE_INFINITY
Value represents a Positive infinity.
positive-infinity-example.js
let a = 1 / 0;

console.log(a); // Infinity

console.log( Number.POSITIVE_INFINITY ); // Infinity

console.log( a == Number.POSITIVE_INFINITY); // true

4. Static methods

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The Number class offers you some very useful static methods:
  • Number.isNaN(number)
  • Number.isFinite(number)
  • Number.isInteger(number)
  • Number.isSafeInteger(number)
  • Number.parseFloat(string)
  • Number.parseInt(string)
This is a static method, which helps check if the a value is NaN (Not a Number).
isNaN-example.js
console.log( Number.isNaN(10) ); // false

let a = "A String" / 100;
console.log(a); // NaN
console.log( typeof a ); // number
console.log( Number.isNaN(a) ); // true

let b = new Number("A String");
console.log(b); // [Number: NaN]
console.log( typeof b ); // object

// b is an Object, wrap NaN value!
console.log( Number.isNaN(b) ); // false (!!!)

// Convert to Number-literal:
let b2 = Number(b);

console.log( Number.isNaN( b2 )); // true
Number.isFinite(number)
This is a static method. It helps check if a value is a finite number. The method returns true/false.
isFinite-example.js
let a = 100;

console.log( Number.isFinite(a)); // true

let b = 1 / 0;
console.log( b ); // Infinite

console.log( Number.isFinite(b)); // false

let c = new Number(100);
// c is an Object
console.log( Number.isFinite(c)); // false (!!!)

// Convert c to Number-literal:
let c2 = Number(c);
console.log( Number.isFinite(c2)); // true
Number.isInteger(number)
This is a static method, that helps check if a value is an integer. The method returns true/false.
isInteger-example.js
console.log(Number.isInteger(0));         // true
console.log(Number.isInteger(1));         // true
console.log(Number.isInteger(-100000));   // true

console.log(Number.isInteger(0.1));       // false
console.log(Number.isInteger(Infinity));   // false
console.log(Number.isInteger("10"));      // false
console.log(Number.isInteger(true));      // false
console.log(Number.isInteger(false));     // false

// A Number-object
let a = new Number(100);
console.log(Number.isInteger( a ));     // false (!!!)

// Convert Number-object to Number-literal
let a2 = Number(a);
console.log(Number.isInteger( a2 ));     // true
Number.isSafeInteger(number)
This is a static method, which helps check if a value is an integer and is in the safe range [-(2^53-1), 2^53 -1]. The method returns true/false.
isSafeInteger-example.js
let a = 100;

console.log( Number.isSafeInteger(a) );     // true

let b = Math.pow(2, 54); // 2^54

console.log(  Number.isSafeInteger(b) );   // false
Number.parseFloat(string)
This is a static method, parse a string in parameters and returning a floating point number.
parseFloat-example.js
let aString1 = "100.2";

let a1 = Number.parseFloat(aString1);
console.log(a1); // 100.2

let aString2 = "Hello 100.2";

let a2 = Number.parseFloat(aString2);
console.log(a2); // NaN
Number.parseInt(string)
This is a static method, parse a string in parameters and returning an Integer.
parseInt-example.js
let aString1 = "100.2";

let a1 = Number.parseInt(aString1);
console.log(a1); // 100

let aString2 = "Hello 100.2";

let a2 = Number.parseInt(aString2);
console.log(a2); // NaN

5. Methods

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  • toExponential()
  • toFixed(digits)
  • toLocaleString()
  • toPrecision(precision)
  • toString(radix)
  • valueOf()
toExponential()
Returns a string representing the number in exponential notation.
toExponential-example.js
var a = 510000;

console.log( a.toExponential() ); // 5.1e+5

var b = 123456789;

console.log( b.toExponential() ); // 1.23456789e+8
toFixed(digits)
This method formats a number with a specific number of digits to the right of the decimal. Method returns a String.
Parameter:
  • digits: The number of digits to appear after the decimal point.
toFixed-example.js
let a = 1.234;

console.log ( a.toFixed() ); // 1
console.log ( a.toFixed(2) ); // 1.23
console.log ( a.toFixed(3) ); // 1.234
console.log ( a.toFixed(5) ); // 1.23400
toLocaleString()
This method converts a number object into a human readable string representing the number using the Locale of the environment.
toLocaleString-example.js
// This example tested on Locale VN.

let num = new Number(177.1234);

console.log( num.toLocaleString()); // 177.123
toPrecision(precision)
This method returns a string representing the number object to the specified precision.
Parameter:
  • precision − An integer specifying the number of significant digits.
toPrecision-example.js
let num = 7.12345;

console.log( num.toPrecision() ); // 7.12345
console.log( num.toPrecision(1) ); // 7
console.log( num.toPrecision(2) ); //  7.1

let num2 = 7.98765;

console.log( num2.toPrecision() ); // 7.98765
console.log( num2.toPrecision(1) ); // 8
console.log( num2.toPrecision(2) ); //  8.0
The toString(radix) method returns a string representing the current number in the radix/base system specified by the parameter.
Parameter:
  • radix (base): An integer between 2 and 36 specifying the base to use for representing numeric values. Default is 10.
toString-example.js
var num = new Number(10);

console.log(num.toString()); // 10

console.log(num.toString(2)); // 1010

console.log(num.toString(8)); // 12
valueOf()
This method returns the primitive value of the specified number object.
valueOf-example.js
// Number object:
let num = new Number(10);

console.log(num.valueOf()); // 10
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