CODEWITHSUNDEEP
javascript
Bun
Bun

Reputation: 3137

What is the point of using empty statement in JavaScript?

I tried to search for good resources on empty statement, but it seem like nothing show up. Even on MDN, they don't have much to say about it.

i.e: 

for(var i = 0; i < a.length; a[i++] = 0);

if((a==0) || (b == 0));

I would like to know what are some real examples that one should use empty statements on their project. What are the reason behind it?

Upvotes: 6

Views: 2218

Answers (7)

Thomas
Thomas

Reputation: 3593

none/lazyness. there is absolutely no difference to 

for(var i = 0; i < a.length;) a[i++] = 0;

and just a minimal difference to 

for(var i = 0; i < a.length; i++) a[i] = 0;

the first one is a few ms faster after a few billion iteration steps; aka. premature optimization

EDIT:

if((a==0) || (b == 0));

this makes no sense at all, since it does nothing.

but expresions like 

a==0 || (b=0);

//or maybe sth like this:

//var noop = ()=>void 0;  //FYI

typeof a === "function" || (a = noop);

are pretty useful to me, since they are short, and readable and an additional if-statement doesn't add any value to readability or understanding (at least once you know this pattern).

Upvotes: 2

Frank Bryce
Frank Bryce

Reputation: 8446

My favorite use for it is to wait for a condition to become true.

while ( !condition );
// do what happens once your condition is met

This is nice to read, in my opinion, but the same can be done with { } instead of the empty statement.

Upvotes: 1

Saqib Amin
Saqib Amin

Reputation: 1171

Let us suppose you have two functions X and Y and let us suppose that Y must only be executed when X returns true, in such a situation you will write:

if( X() && Y() );

Upvotes: 0

Bergi
Bergi

Reputation: 665101

The examples you've given don't make much sense. They should better be written

for (var i = 0; i < a.length;) a[i++] = 0;
for (var i = 0; i < a.length; i++) a[i] = 0;
; // the comparisons really don't do anything (assuming a and b are no objects)
(a==0) || (b = 0); // Oh wait, that's the one given by @Shomz
if (a != 0) b = 0;

However, there are real-world applications for the empty statement. I'll just list 3 that come to my mind:

  • function x() {
    …
};

    A semicolon where it doesn't belong (e.g. after the function declaration above) makes an empty statement.

  • ;
…

    A leading semicolon on your script files helps to guard against buggy inclusions or file concatenations.

  • while (!check_for_finish()); // do nothing

    An empty loop body can be used for busy-waiting loops (not recommended) and similar.

Upvotes: 2

frogatto
frogatto

Reputation: 29285

The first example for(var i = 0; i < a.length; a[i++] = 0); is useful IMO, and the reasons would be:

  • Writing less without sacrificing readability.
  • beauty!
  • Telling people: Hey, I'm a pro JS coder. :)

The second one if((a==0) || (b == 0)); seems doesn't nothing.

Upvotes: 0

Marco Altieri
Marco Altieri

Reputation: 3818

I do not think that they are really useful, but I can be wrong. One can try to use side effects of the evaluation of the conditions in an if, but I do not see a good reason to do so.

Upvotes: 1

Shomz
Shomz

Reputation: 37701

The first one obviously loops through the array and assigns all values to zero, without having the code specified in the statement.

The other one seems like a typo, because it is useless.

However, something like 

if((a==0) || (b = 0));

would make sense, as it would assign b to zero in case a is not zero.

var a = 1, b = 1;
if((a == 0) || (b = 0));

alert("a: " + a + ", b: " + b);

Upvotes: 1

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