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Truth, the final frontier.

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  Truth, the final frontier. "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2019-05-25 12:29 +0200
    Re: Truth, the final frontier. John G Harris <niam@jghnorth.org.uk.invalid> - 2019-05-25 11:40 +0100
    Re: Truth, the final frontier. Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2019-05-25 23:40 +0200

#36646 — Truth, the final frontier.

Truth, the final frontier:

console.log( 'This is: ', .1 + .2 != .3 ); 
// This is: true

More here:
<https://0.30000000000000004.com/>

===========

However:

console.log( 'This is: ' + .1 + .2 );
// This is: 0.10.2

-- 
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

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#36647

On Sat, 25 May 2019 12:29:16 +0200, "Evertjan."
<exxjxw.hannivoort@inter.nl.net> wrote:

>Truth, the final frontier:
>
>console.log( 'This is: ', .1 + .2 != .3 ); 
>// This is: true
>
>More here:
><https://0.30000000000000004.com/>

A well-known gotcha. If anyone complains remind them that answers are
very accurate : enough to measure the relativity effect of someone
cycling past you.


>===========
>
>However:
>
>console.log( 'This is: ' + .1 + .2 );
>// This is: 0.10.2

Another well-known gotcha. The compiler is being "helpful".

  John

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#36649

Evertjan. wrote:
> Truth, the final frontier:
> 
> console.log( 'This is: ', .1 + .2 != .3 ); 
> // This is: true
> 
> More here:
> <https://0.30000000000000004.com/>

(This is NOT the Web.  Tell news.)

Floating-point arithmetic:

{0.1, 0.2, 0.3} ∩ {b | b =  ∑   m × 2^i; m ∈ {0, 1}} = ∅.
                          i ∈ ℤ

0.1 = 2^-4 + 2^-5 + 2^-8 + … = 0.0625 + 0.03125 + 0.00390625 + …
0.2 = 2^-3 + 2^-4 + 2^-7 + … = 0.125  + 0.0625  + 0.0078125  + …
0.3 = 2^-2 + 2^-5 + 2^-6 + … = 0.25   + 0.03125 + 0.015625   + …

> However:
> 
> console.log( 'This is: ' + .1 + .2 );
> // This is: 0.10.2

The second statement is fundamentally different from the first statement in
that the method call has only *one* argument.  Thus, the expression in the
argument is the result of *string concatenation*.

As those know who have been subscribed to this newsgroup for, say, more than
6 months, if the binary (by contrast to unary) “+” operator is used and one
of the operands evaluates to a String value, then all operands are converted
to String before *string concatenation* is performed:

  1. 'This is: ' + .1              + .2
     ^^^^^^^^^^^   ^^                ^^
        String     Number            Number

  2. 'This is: ' + (.1).toString() + (.2).toString
  3. 'This is: ' + '0.1'           + '0.2'
  4. 'This is: 0.10.2'

By contrast:

| >  console.log('This is: ' + (.1 + .2));
|    This is: 0.30000000000000004
|
| >  console.log('This is: ', .1 + .2);
|    This is:  0.30000000000000004
|
| >  navigator.userAgent
| <- "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko)
| Chrome/57.0.2987.98 Safari/537.36"

∎

Note that console.log() will automatically output a space character between
the evaluation results of its arguments.

Get a real name and address.

-- 
PointedEars

Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.

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