Playing with JS #1: Numbers

In this article you will learn about numbers. But what is a number in JavaScript?

Number

The primitive wrapper object Number is used to represent numbers like 42 or -18.

The number type in JavaScript is represented as a 64-bit floating point (same as Java's Double). There is no separate integer type, so 1 and 1.0 are the same value.

It's practical but it can reveal some strange things.

The basics

Let's play with that primitive wrapper.

Number(0) // 0
Number('12') // 12
Number(true) // 1
Number('hello') // NaN (not a number)
Number() // 0
Number(undefined) // NaN

As you can see, some results can be disturbing. Passing nothing to the constructor works but undefined returns NaN.

This is only the beginning! Let's play with some arithmetic operations.

The weirdos

true + true // 2
0.1 + 0.2 // 0.30000000000000004
10000000000000000 + 1 // 10000000000000000

Let's dig a bit into those weird results.

• true + true equals 2 because Number(true) is 1.
• 0.1 + 0.2 equals 0.30000000000000004 because JavaScript follows a 64-bit floating point representation for numbers. With decimal fractions, this floating-point number system causes some rounding errors in JavaScript. Learn more about that
• 10000000000000000 + 1 equals 10000000000000000 because we are above the precision limit of double-precision floating-point so it is rounded to the nearest double-precision value.

The cool (and useful) things

Get timestamp from a datetime

Number(new Date()) // Timestamp of current datetime

Make numbers more readable

Number(1000000000).toLocaleString('en-US') // '1,000,000,000'
Number(1000000000).toLocaleString('fr-FR') // '1 000 000 000'
Number(1000000000).toLocaleString(navigator.language)

The theory

Properties

• Number.EPSILON is the smallest interval between two representable numbers
• Number.MAX_SAFE_INTEGER and Number.MIN_SAFE_INTEGER are the maximum and minimum safe integer
• Number.MIN_VALUE and Number.MAX_VALUE are the smallest and largest positive representable number
• Number.NaN is a value used to represent something that is not a number.
• Number.NEGATIVE_INFINITY and Number.POSITIVE_INFINITY - Values representing negative and positive infinity

Methods

• Number.isNaN(value) returns true if the value is not a number
• Number.isFinite(value) returns true if the value is finite
• Number.isInteger(value) returns true if the value is an integer
• Number.isSafeInteger(value) returns true if the value is a safe integer (number between -(2^53 - 1) and 2^53 - 1)
• Number.parseFloat(value) parses the value and returns a floating point number. If a number cannot be parsed from the argument, it returns NaN
• Number.parseInt(value, [radix]) parses a string argument and returns an integer of the specified radix or base.

Instance methods

• Number().toExponential(digits) returns a string representing the number in exponential notation
• Number().toFixedPoint(digits) returns a string representing the number in fixed-point notation
• Number().toLocaleString([locales], [, options]) returns a string with a language sensitive representation of this number
• Number().toPrecision(precision) returns a string representing the number to a specified precision in fixed-point or exponential notation
• Number().toString(radix) returns a string representing the specified object in the specified radix
• Number().valueOf() returns the primitive value of the specified object

The sources

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number
• https://medium.com/@surender.neelakantan/funny-javascript-7-little-questions-8af0b4ca25a2
• https://github.com/denysdovhan/wtfjs
• https://www.oreilly.com/library/view/javascript-the-good/9780596517748/
• https://gauravkk22.medium.com/why-0-1-0-2-0-3-is-false-in-js-mystery-unsolved-with-solution-4f7db2755f18