arrayLikeType (rkatic)

HTML

<ul id="log"></ul>

CSS

li.pass { background: #02C500; }
li.fail { background: red; }

JavaScript

var valids = {
    "array like object": { length: 3, 0: "a", 1: "b", 2: "c" },
    "empty array-like object": { length: 0 }
};
    
for ( msg in valids ) {
   var obj = valids[ msg ];
    
   var keys = $.map( obj, function( v, k ) {
        return k;
   });
    
   var pass = keys.length === obj.length;
   
   $("<li>").text( msg ).addClass( pass ? "pass" : "fail" ).appendTo("#log");
}