Number Methods

Question 1

The toString() Method
The toString() method returns a number as a string.

All number methods can be used on any type of numbers (literals, variables, or expressions):

var x = 123;
// returns 123 from variable x
// returns 123 from literal 123
// returns 123 from expression 100 + 23

Answer 1

var x = 123;
x.toString();            // returns 123 from variable x
(123).toString();        // returns 123 from literal 123
(100 + 23).toString();   // returns 123 from expression 100 + 23

var x = 123;
document.getElementById("demo").innerHTML =
  x.toString() + "<br>" +
   (123).toString() + "<br>" +
   (100 + 23).toString();

Question 2

The toExponential() Method
toExponential() returns a string, with a number rounded and written using exponential notation.

A parameter defines the number of characters behind the decimal point:

var x = 9.656;
// returns 9.66e+0
// returns 9.6560e+0
// returns 9.656000e+0

Answer 2

var x = 9.656;

x. toExponential(2); // returns 9.66e+0
x. toExponential(4); // returns 9.6560e+0
x. toExponential(6); // returns 9.656000e+0

var x = 9.656;

document. getElementById(“demo”).innerHTML =
x. toExponential() + “<br></br>” +
x. toExponential(2) + “<br></br>” +
x. toExponential(4) + “<br></br>” +
x. toExponential(6);

The parameter is optional. If you don’t specify it, JavaScript will not round the number.

Question 3

The toFixed() Method
toFixed() returns a string, with the number written with a specified number of decimals:

Example
var x = 9.656;
// returns 10
// returns 9.66
// returns 9.6560
// returns 9.656000

toFixed(2) is perfect for working with money.

Answer 3

var x = 9.656;

document. getElementById(“demo”).innerHTML =
x. toFixed(0) + “<br></br>” +
x. toFixed(2) + “<br></br>” +
x. toFixed(4) + “<br></br>” +
x. toFixed(6);

The toFixed() method rounds a number to a given number of digits.

For working with money, toFixed(2) is perfect.

Question 4

The toPrecision() Method
toPrecision() returns a string, with a number written with a specified length:

var x = 9.656;
// returns 9.656
// returns 9.7
// returns 9.656
// returns 9.65600

Answer 4

var x = 9.656;

document. getElementById(“demo”).innerHTML =
x. toPrecision() + “<br></br>” +
x. toPrecision(2) + “<br></br>” +
x. toPrecision(4) + “<br></br>” +
x. toPrecision(6);

Question 5

Converting Variables to Numbers
There are 3 JavaScript methods that can be used to convert variables to numbers:

The Number() method
The parseInt() method
The parseFloat() method
These methods are not number methods, but global JavaScript methods.

Answer 5

Global JavaScript Methods
JavaScript global methods can be used on all JavaScript data types.

These are the most relevant methods, when working with numbers:

Method Description
Number() Returns a number, converted from its argument.
parseFloat() Parses its argument and returns a floating point number
parseInt() Parses its argument and returns an integer

Question 6

The Number() Method
Number() can be used to convert JavaScript variables to numbers:

Example
Number(true);          // returns 1
Number(false);         // returns 0
Number("10");          // returns 10
Number("  10");        // returns 10
Number("10  ");        // returns 10
Number(" 10  ");       // returns 10
Number("10.33");       // returns 10.33
Number("10,33");       // returns NaN
Number("10 33");       // returns NaN 
Number("John");        // returns NaN

Answer 6

document.getElementById("demo").innerHTML = 
  Number(true) + "<br>" +
  Number(false) + "<br>" +
  Number("10") + "<br>" + 
  Number("  10") + "<br>" +
  Number("10  ") + "<br>" +
  Number(" 10  ") + "<br>" +
  Number("10.33") + "<br>" + 
  Number("10,33") + "<br>" +
  Number("10 33") + "<br>" +
  Number("John");

If the number cannot be converted, NaN (Not a Number) is returned.

Number() can also convert a date to a number:

Number(new Date("2017-09-30"));    // returns 1506729600000
The Number() method above returns the number of milliseconds since 1.1.1970.

Question 7

The parseInt() Method
parseInt() parses a string and returns a whole number. Spaces are allowed. Only the first number is returned:

parseInt("10");         // returns 10
parseInt("10.33");      // returns 10
parseInt("10 20 30");   // returns 10
parseInt("10 years");   // returns 10
parseInt("years 10");   // returns NaN

Answer 7

The global JavaScript function parseInt() converts strings to numbers:

document.getElementById("demo").innerHTML = 
  parseInt("10") + "<br>" +
  parseInt("10.33") + "<br>" +
  parseInt("10 6") + "<br>" +  
  parseInt("10 years") + "<br>" +  
  parseInt("years 10");  

If the number cannot be converted, NaN (Not a Number) is returned.

Question 8

The parseFloat() Method
parseFloat() parses a string and returns a number. Spaces are allowed. Only the first number is returned:

parseFloat("10");        // returns 10
parseFloat("10.33");     // returns 10.33
parseFloat("10 20 30");  // returns 10
parseFloat("10 years");  // returns 10
parseFloat("years 10");  // returns NaN

Answer 8

The parseFloat() method converts strings to numbers:

document.getElementById("demo").innerHTML = 
  parseFloat("10") + "<br>" +
  parseFloat("10.33") + "<br>" +
  parseFloat("10 6") + "<br>" +  
  parseFloat("10 years") + "<br>" +
  parseFloat("years 10");    

If the number cannot be converted, NaN (Not a Number) is returned.

Question 9

Number Properties
Property Description

MAX_VALUE Returns the largest number possible in JavaScript

MIN_VALUE Returns the smallest number possible in JavaScript

POSITIVE_INFINITY Represents infinity (returned on overflow)

NEGATIVE_INFINITY Represents negative infinity (returned on overflow)

NaN Represents a “Not-a-Number” value

JavaScript MIN_VALUE and MAX_VALUE

MAX_VALUE returns the largest possible number in JavaScript.

MIN_VALUE returns the lowest possible number in JavaScript.

JavaScript POSITIVE_INFINITY

POSITIVE_INFINITY is returned on overflow:

JavaScript NEGATIVE_INFINITY

NEGATIVE_INFINITY is returned on overflow:

JavaScript 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):

Number Properties Cannot be Used on Variables
Number properties belongs to the JavaScript’s number object wrapper called Number.
These properties can only be accessed as Number.MAX_VALUE.
Using myNumber.MAX_VALUE, where myNumber is a variable, expression, or value, will return undefined:

Answer 9

var x = Number.MAX_VALUE;

var x = Number.MIN_VALUE;

var x = Number.POSITIVE_INFINITY;

var x = 1 / 0;

var x = Number.NEGATIVE_INFINITY;

var x = -1 / 0;

var x = Number.NaN;

var x = 100 / “Apple”; // x will be NaN (Not a Number)

var x = 6;
var y = x.MAX_VALUE;    // y becomes undefined