I usually check if a collection exists before iterating over it:
var a1 = [1,2,3], a2;
if(a1){
$.each(a1, function(k, v){
console.log(v);
});
}
I thought a bit about an inline solution and came up with this:
!a1 || $.each(a1, function(k, v){
console.log(v);
});
Which seems to work fine. Any downsides or alternatives?
Without the check I would get a Uncaught TypeError: Cannot read property 'length' of undefined exception.
You can of course use the || operator in another way like this:
$.each(a2 || {}, function(k, v){
console.log(v);
});
or
$.each(a2 || [], function(k, v){
console.log(v);
});
a2 || {}?
a2 is defined, the whole expression evaluates to a defined object and stops without checking further the {}, then that object is passed in the $.each and it runs normally. Otherwise when a2 is not defined, the whole expression's value depends on the remaining part which is {}, that part is of course defined and it stops returning that empty object. With that empty object passed in $.each, there is in fact no internal loop at all.!a1 || $.each(a1, function(k, v){ console.log(v); }); run faster than yours, given that he is doing the empty object check before the call to $.each?
a1 = a1 || []then do the iteration. But first solution is readable and maintainable, second solution is just not worth it. In any case you'd doa1 && $.each