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?

Answer 1

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.

Answer 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).

Answer 3

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);