html - Arrays with 'named' constructors in JavaScript? (e.g HTMLCollection) -

consider following 2 ways of creating instance of object:

function f() { return { k: 'v'} } var inst1 = f();  function f() { this.k = 'v'; }  var inst2 = new f(); 

the behavior of inst1 , inst2 same, difference different constructor saved object:

inst1.constructor; // object() inst2.constructor; // f() 

what's constructor of array? see:

var xs = []; xs.constructor; // array() 

until point understand logic. bumped following:

var tags = document.getelementsbytagname("*"); typeof tags; // object tags.constructor; // htmlcollection() 

so far it's similar inst2 example. when console.log firebug, receive array 'named' constructor:

console.log(tags); // htmlcollection[tag1, tag2, ...] 

the block brackets confuse me, have expected curly 1 here. there must explanation this, knows answer?

it sounds crux of question lies in determining how firebug displays object. firebug examines objects passed it, , chooses how display objects string based on properties have.

htmlcollection "array-like" has length property, , stores contents in properties named 0, 1, 2, etc. makes array-like , firebug recognizes this, outputting string representation of object array.

in case of firebug, if sees length , splice property, treat object array-like:

var myarraylike = function(){     this[0] = 1;     this.length = 1;     this.splice = function(){}; } 

firebug output:

-> new myarraylike(); <- [1]