Question

which of the following are valid object constructors?

1) var m = function(){}
2) m = function(){}
3) m.prototype.constructor = function(){}

Answer 1

They all appear to be valid statements that declare an empty function, and assign it to different variables.

Every function in Javascript is both an object itself (or f.prototype wouldn’t work) and a potential object constructor. Any function may be called with the new Thingy syntax (or perhaps new m in your example). Or it could be called normally – the only special thing new does is set this to an object derived from f.prototype.

A newly created function has a prototype property that contains a newly minted object ({}), which has no properties except a hidden constructor property pointing at the function (it’s a circular reference, actually)

It should be true that:

var m = function(){};
m.prototype.constructor == m;