How to check if a Javascript function is a constructor

Question

I noticed not all the Javascript functions are constructors.

var obj = Function.prototype;
console.log(typeof obj === \'function\'); //true
obj(); //OK
new          


        

Answer 1

If the function is a constructor then it will have a "prototype" member which in turn has a "constructor" member that is equal to the function itself.

function isConstructor(func) {
    return (func && typeof func === "function" && func.prototype && func.prototype.constructor) === func;
}