What is the point of using empty statement in JavaScript?

Question

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?

let me quote from the code comment just above the for loop: `// Assign all array values to 0` — Aprillion, Jan 17 '16 at 16:29
It is helpful for [code golf](http://codegolf.stackexchange.com). For example this saves 2 bytes because you don't need a code block wrapped in brackets `{}`: `for(a=0;a++<100;b=a,c=b+a);` — insertusernamehere, Jan 17 '16 at 18:42

Thomas · Answer 1 · 2016-01-17T17:53:50.283

2

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).

edited Jan 17 '16 at 17:53

answered Jan 17 '16 at 16:31

Thomas

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Have you tested it? I'm pretty sure it is *not* faster. – Bergi Jan 17 '16 at 16:45
yeah, it's because in `a[i++]=0` i++ (increment and getting the value of i) are processed as one instruction, whilst in `a[i]=0; i++;` they are two; but as i said, premature optimizations. Every function-call or deoptimized function, and so much more has a way higher impact on performance than this optimization. – Thomas Jan 17 '16 at 17:37
What "instruction" do you mean? You cannot just count JS tokens. – Bergi Jan 17 '16 at 18:43

score 2 · Accepted Answer · edited May 23 '17 at 11:59

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.

Shomz · Answer 3 · 2016-01-17T16:32:50.413

1

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);

edited Jan 17 '16 at 16:32

answered Jan 17 '16 at 16:31

Shomz

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you have strange definition of `make sense` - `if(a===0) b=0;` or even `b = (a===0 ? 0 : b)` are both more readable IMO – Aprillion Jan 17 '16 at 16:32
Obviously not a recommended practice nor something I'd suggest nor something that I'd write, but **an answer to the question**. There are assignments in conditionals, probably more than you'd expect to see. Coming up with more readable variations would be irrelevant and exhausting here. Focus on the question. – Shomz Jan 17 '16 at 16:34
please allow me to add an emphasis to the OP's question: "real examples that one **should** use empty statements" – Aprillion Jan 17 '16 at 16:36
Sorry, I either missed that part, or it was edited while I was writing the answer. – Shomz Jan 17 '16 at 16:41

score 1 · Answer 4 · answered Jan 17 '16 at 16:34

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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.

answered Jan 17 '16 at 16:34

Marco Altieri

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score 1 · Answer 5 · answered Jan 17 '16 at 17:27

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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.

answered Jan 17 '16 at 17:27

Frank Bryce

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score 0 · Answer 6 · answered Jan 17 '16 at 16:42

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.

score 0 · Answer 7 · answered Jan 17 '16 at 16:49

0

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() );

answered Jan 17 '16 at 16:49

Saqib Amin

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No. You would write `if (X()) Y();` (or `X() && Y();`). No empty statement. – Bergi Jan 17 '16 at 16:50
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Why not `X() && Y()`? – Oriol Jan 17 '16 at 16:51

What is the point of using empty statement in JavaScript?

7 Answers7