explain javascript code

Question

1.00/5 (1 vote)

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can you please explain this code

JavaScript

var demo = (y1 & 1) ? x1 + 0.5 : x1;

or convert it to python because i know python

thank you

Posted 3-Nov-14 1:32am

Member 11202368

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Comments

Kornfeld Eliyahu Peter 3-Nov-14 7:49am

It is hard to believe that python version will help you anyway - but...
demo = (y1 & 1) if x1 + 0.5 else x1

Member 11202368 3-Nov-14 19:56pm

thanks for reply, i want to use this code in python but i have no idea about js

3 solutions

Solution 2

I am not sure if this is really Python or JavaScript related. And as you proclaimed your Python (or any other programming language), it should have been understandable.

Anyway, here is the pseudo-code:

JavaScript

if (y1 & 1) is true
{
	demo = x1 + 0.5;
}
else
{
	demo = x1;
}

Posted 3-Nov-14 1:50am

Manas Bhardwaj

Updated 3-Nov-14 5:10am

v2

Comments

Sergey Alexandrovich Kryukov 3-Nov-14 11:14am

Sorry, Manas. This is incorrect. The expression in the brackets checks up if the 1st bit of y1 is set.
Please see Solution 3.
—SA

Member 11202368 3-Nov-14 20:15pm

thank you

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DamithSL · Accepted Answer · 2014-11-03T01:46:00

Solution 1

why not read some documentation and try to understand it?
Conditional (Ternary) Operator (?: ) [^]
JavaScript Operators[^]

Posted 3-Nov-14 1:46am

DamithSL

Comments

Sergey Alexandrovich Kryukov 3-Nov-14 11:15am

Fully agree, a 5.
However, I decided to answer in detail, but only to compensate for confusing Solution 2, which is incorrect.
Please see Solution 3.
—SA

DamithSL 3-Nov-14 11:51am

Thank you, SA

Manas Bhardwaj 3-Nov-14 11:41am

Yes +5!

DamithSL 3-Nov-14 11:51am

Thank you, Manas

Maciej Los 3-Nov-14 11:52am

+5!

DamithSL 3-Nov-14 11:53am

Thank you, Maciej

Member 11202368 3-Nov-14 19:57pm

thank you all of you, i know nothing about js!! i asked in python because i know python

Sergey Alexandrovich Kryukov · Accepted Answer · 2014-11-03T05:13:00

Solution 3

Solution 2 is not quite correct.

The corrected pseudo-code is:

C#

if (first bit (#0) in y1 is set)
{ // if this bit is set:
    demo = x1 + 0.5;
} 
else 
{ // if this bit is clear:
    demo = x1;
}

The bit check is done by the bitwise AND operator '&': test number y1 is compared with a bit mask with a single bit installed (1, 2, 4, 8, etc.) and the result is either 0 or not.
Now, the trick is: if the operand of "if" is a number, it behaves as False if the number is 0, True in all other cases; this is a dirty C-like convention.

Please see, for example, https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_Operators[^].

—SA

Posted 3-Nov-14 5:13am

Sergey Alexandrovich Kryukov

Updated 3-Nov-14 16:31pm

v4

Comments

DamithSL 3-Nov-14 11:29am

5wd, Very nicely explained

Sergey Alexandrovich Kryukov 3-Nov-14 12:25pm

Thank you, Damith,
—SA

Manas Bhardwaj 3-Nov-14 11:41am

Thanks for your comment on my solution. Yes, I overlooked that.

+5!

Sergey Alexandrovich Kryukov 3-Nov-14 12:25pm

Thank you Manas.
—SA

Maciej Los 3-Nov-14 11:53am

+5!

Sergey Alexandrovich Kryukov 3-Nov-14 12:26pm

Thank you, Maciej.
—SA

Member 11202368 3-Nov-14 20:15pm

thank you, please explain this "first but (#0) in y1 is set"
i think this code is more complex than i thought

Sergey Alexandrovich Kryukov 3-Nov-14 22:10pm

I mistyped "bit" — should be "first bit (#0) in y1 is set". Sorry for the inconvenience. Fixed.

I explained it in next two sentences after the pseudo-code sample. It uses 1 as a bitmask (bit #0 is set, others are cleared). When you do bitwise AND with the mask, it reveals if the bit in v1 is set or clear. I'm adding more comments to the pseudo-code. When you get it, please accept the answer formally (green "Accept" button). Any follow-up questions will be welcome anyway.
—SA