What does the JSLint error 'body of a for in should be wrapped in an if statement' mean?

Question

I used JSLint on a JavaScript file of mine. It threw the error:

for( ind in evtListeners ) {

Problem at line 41 character 9:

Answer 1

Just to add on to the topic of for in/for/$.each, I added a jsperf test case for using $.each vs for in: http://jsperf.com/each-vs-for-in/2

Different browsers/versions handle it differently, but it seems $.each and straight out for in are the cheapest options performance-wise.

If you're using for in to iterate through an associative array/object, knowing what you're after and ignoring everything else, use $.each if you use jQuery, or just for in (and then a break; once you've reached what you know should be the last element)

If you're iterating through an array to perform something with each key pair in it, should use the hasOwnProperty method if you DON'T use jQuery, and use $.each if you DO use jQuery.

Always use for(i=0;i if you don't need an associative array though... lol chrome performed that 97% faster than a for in or $.each