4.2.2 JS Number Methods

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):

Example 1: JS Number Methods part 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

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:

Example 2: JS Number Methods part 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

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

The toFixed() Method

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

Example 3: JS Number Methods part 3

var x = 9.656;
x.toFixed(0);           // returns 10
x.toFixed(2);           // returns 9.66
x.toFixed(4);           // returns 9.6560
x.toFixed(6);           // returns 9.656000

toFixed(2) is perfect for working with money.

The toPrecision() Method

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

Example 4: JS Number Methods part 4

var x = 9.656;
x.toPrecision();        // returns 9.656
x.toPrecision(2);       // returns 9.7
x.toPrecision(4);       // returns 9.656
x.toPrecision(6);       // returns 9.65600

The valueOf() Method

valueOf() returns a number as a number.

Example 5: JS Number Methods part 5

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

• In JavaScript, a number can be a primitive value (typeof = number) or an object (typeof = object).
• The valueOf() method is used internally in JavaScript to convert Number objects to primitive values.
• There is no reason to use it in your code.

All JavaScript data types have a valueOf() and a toString() method.

The Number() Method

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

Example 6: JS Number Methods part 6

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

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

The Number() Method Used on Dates

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

Example 7: JS Number Methods part 7

Number(new Date("2017-09-30"));    // returns 1506729600000

The Number() method above returns the number of milliseconds since 1.1.1970.

The parseInt() Method

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

Example 8: JS Number Methods part 8

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

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

The parseFloat() Method

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

Example 9: JS Number Methods part 9

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

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

JavaScript MIN_VALUE and MAX_VALUE

MAX_VALUE returns the largest possible number in JavaScript.

Example 10: JS Number Methods MAX_VALUE Property

var x = Number.MAX_VALUE;

MIN_VALUE returns the lowest possible number in JavaScript.

Example 11: JS Number Methods MIN_VALUE Property

var x = Number.MIN_VALUE;

JavaScript POSITIVE_INFINITY

Example 12: JS Number Methods POSITIVE_INFINITY Property part 1

var x = Number.POSITIVE_INFINITY;

POSITIVE_INFINITY is returned on overflow:

Example 13: JS Number Methods POSITIVE_INFINITY Property part 2

var x = 1 / 0;

JavaScript NEGATIVE_INFINITY

Example 14: JS Number Methods NEGATIVE_INFINITY Property part 1

var x = Number.NEGATIVE_INFINITY;

NEGATIVE_INFINITY is returned on overflow:

Example 15: JS Number Methods NEGATIVE_INFINITY Property part 2

var x = -1 / 0;

JavaScript NaN - Not a Number

Example 16: JS Number Methods NaN part 1

var x = Number.NaN;

• 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):

Example 17: JS Number Methods NaN part 2

var x = 100 / "Apple";  // x will be 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:

Example 18: JS Number Methods Number Properties

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