basic Javascript if/else statement question

Question

I'm looking at the following Javascript code, trying to port it to another language:

if (x>n) {return q} {return 1-q)

I don't know what the code is doing, but can someone tell me based on syntax what occurs? Is there an implied 'else' before the last set of {}? That is, if x>n then return q otherwise return 1-q?

If it helps, here's the line of code it was embedded within:

if(x>9000 | n>6000) { var q=Norm((Power(x/n,2/5)+1/(8*n)-1)/Sqrt(9/(2*n)))/3; if (x>n) {return q}{return 1-q} }

thanks

@Jacob Relkin It could be from a compressed java script library i.e. thrown out all spaces and newlines to minimize file size. — Sem Vanmeenen
– Sem Vanmeenen, Commented Feb 17, 2011 at 0:38
@SemVanmeenen Except it hasn't thrown out all meaningless spaces :P — alex
– alex, Commented Feb 17, 2011 at 0:40
Unless I'm unaware of something it looks to me like that code is broken. Pop open firebug console: if (1>2) {1} {2} prints 2, all good. if (3>2) {1} {2} prints 2... OK...? if (3>2) {1} else {2} prints 1. — Endophage
– Endophage, Commented Feb 17, 2011 at 0:42

Ken Wayne VanderLinde · Accepted Answer · 2011-02-17 00:38:23Z

2

There is not an implied 'else', the next set of braces simply defines another compound statement. In this case, it acts like an 'else', but only because the 'if' portion carries a return statement.

answered Feb 17, 2011 at 0:38

Ken Wayne VanderLinde

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Comments

Xavier Holt · Accepted Answer · 2011-02-17 00:43:46Z

There's only an implied else because the block that pairs with the if statement returns from the function. The code you posted is equivalent to:

if(x > n)
{
    return q;
}
return q + 1;

You only get if/else-like behaviour because the second statement can only be executed if the first statement isn't (because the first statement would return from the function, and control would never get to the second).

This bad code! For readability / maintainability / sanity, it should be written in one of these more sustainable formats:

if(x > n) {return q;}
else      {return q + 1;}

Or:

return (x > n)? q : q + 1;

Hope that helps!

Daniel A. White · Accepted Answer · 2011-02-17 00:36:48Z

1

Its basically this:

if (x>n)
   return q; 
else 
   return 1-q;

answered Feb 17, 2011 at 0:36

Daniel A. White

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4 Comments

baash05 Over a year ago

beautifully answered. Simple as.

Xavier Holt Over a year ago

Not true! It only happens to work because the if block returns. Anything else, say if(x > n) {x += 12} {x +=7}, will behave completely differently. There is not an implied else.

Daniel A. White Over a year ago

@Xavier - it is with the return.

Xavier Holt Over a year ago

True, but I think this is a dangerous answer to the more general question of "Does if(x) {block-1} {block-2} evaluate as if(x) {block-1} else {block-2}?" You're right in this specific case, but making that assumption globally (which your answer seems to propound) will bite you as soon as block-1 doesn't have a return statement.

Amy Anuszewski · Accepted Answer · 2011-02-17 00:36:49Z

1

There's an implied else. If x>n, the function returns q. Otherwise, it goes to the next return statement and returns 1-q.

answered Feb 17, 2011 at 0:36

Amy Anuszewski

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2 Comments

Day Over a year ago

Slightly misleading to say "implied else". If there was no return in the if clause, both clauses would be executed when the test evaluates to true. See jsfiddle.net/daybarr/jJCGE for code

Amy Anuszewski Over a year ago

With that first return there, the second return would only be reached if the if statement was false. Hence, the implication of an else. It's stylistically bad, but what he was asking for was the meaning - what would happen if the code executed. I hope his rewrite would be better code. ;-)

Delta · Accepted Answer · 2011-02-17 00:41:22Z

1

That block of {} after return q is not necessary. there isn't any else statement implied there, it's just that if it passes throught the if statement and return q, what comes next won't be executed anymore, otherwise, it will. Then there is no need to put an else there.

answered Feb 17, 2011 at 0:41

Delta

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Comments

alex · Accepted Answer · 2011-12-28 23:04:22Z

1

That code is really...

if (x > 9000 | n > 6000) {
    var q = Norm((Power(x / n, 2 / 5) + 1 / (8 * n) - 1) / Sqrt(9 / (2 * n))) / 3;
    if (x > n) {
        return q
    } {
        return 1 - q
    }
}

Either someone thinks unreadable code is a good idea, or they used a bad minifer.

edited Dec 28, 2011 at 23:04

answered Feb 17, 2011 at 0:38

alex

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