JavaScript Reference: Number

This article documents how to work with the Number built-in object, and lists its properties and methods.

A number value can be generated using a number literal syntax:

const age = 36
typeof age //number

or using the Number global function:

const age = Number(36)
typeof age //number

If we add the new keyword, we get a Number object in return:

const age = new Number(36)
typeof age //object

which has a very different behavior than a number type. You can get the original number value using the valueOf() method:

const age = new Number(36)
typeof age //object
age.valueOf() //36

Properties

EPSILON the smallest interval between two numbers
MAX_SAFE_INTEGER the maximum integer value JavaScript can represent
MAX_VALUE the maximum positive value JavaScript can represent
MIN_SAFE_INTEGER the minimum integer value JavaScript can represent
MIN_VALUE the minimum positive value JavaScript can represent
NaN a special value representing “not a number”
NEGATIVE_INFINITY a special value representing negative infinity
POSITIVE_INFINITY a special value representing positive infinity

Those properties evaluated to the values listed below:

Number.EPSILON
Number.MAX_SAFE_INTEGER
Number.MAX_VALUE
Number.MIN_SAFE_INTEGER
Number.MIN_VALUE
Number.NaN
Number.NEGATIVE_INFINITY
Number.POSITIVE_INFINITY

2.220446049250313e-16
9007199254740991
1.7976931348623157e+308
-9007199254740991
5e-324
NaN
-Infinity
Infinity

Object Methods

We can call those methods passing a value:

Number.isNaN(value): returns true if value is not a number
Number.isFinite(value): returns true if value is a finite number
Number.isInteger(value): returns true if value is an integer
Number.isSafeInteger(value): returns true if value is a safe integer
Number.parseFloat(value): converts value to a floating point number and returns it
Number.parseInt(value): converts value to an integer and returns it

I mentioned “safe integer”. Also up above, with the MAX_SAFE_INTEGER and MIN_SAFE_INTEGER properties. What is a safe integer? It’s an integer that can be exactly represented as an IEEE-754 double precision number (all integers from (2^53 - 1) to -(2^53 - 1)). Out of this range, integers cannot be represented by JavaScript correctly. Out of the scope of the course, but here is a great explanation of that.

Instance methods

When you use the new keyword to instantiate a value with the Number() function, we get a Number object in return:

const age = new Number(36)
typeof age //object

This object offers a few unique methods you can use. Mostly to convert the number to specific formats.

.toExponential(): return a string representing the number in exponential notation
.toFixed(): return a string representing the number in fixed-point notation
.toLocaleString(): return a string with the local specific conventions of the number
.toPrecision(): return a string representing the number to a specified precision
.toString(): return a string representing the specified object in the specified radix (base). Overrides the Object.prototype.toString() method
.valueOf(): return the number primitive value of the object