JavaScript Reference: Number
All about the JavaScript Number properties and methods
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 numbersMAX_SAFE_INTEGER
the maximum integer value JavaScript can representMAX_VALUE
the maximum positive value JavaScript can representMIN_SAFE_INTEGER
the minimum integer value JavaScript can representMIN_VALUE
the minimum positive value JavaScript can representNaN
a special value representing “not a number”NEGATIVE_INFINITY
a special value representing negative infinityPOSITIVE_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 ifvalue
is not a numberNumber.isFinite(value)
: returns true ifvalue
is a finite numberNumber.isInteger(value)
: returns true ifvalue
is an integerNumber.isSafeInteger(value)
: returns true ifvalue
is a safe integerNumber.parseFloat(value)
: convertsvalue
to a floating point number and returns itNumber.parseInt(value)
: convertsvalue
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
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