Question

Code snippet is following, Can anyone explain why a.hasOwnProperty("prototype") is true, the others are false? Does it mean function has its own prototype, the others are inherited from Object?If so, why c.hasOwnProperty("prototype") is false? Besides, where does property of their constructor property come from? Thanks

    var a = function () {
    };
    var b = new String("test");
    var c = {};

    console.log(a.hasOwnProperty("prototype"));//true
    console.log(b.hasOwnProperty("prototype"));//false
    console.log(c.hasOwnProperty("prototype"));//false
    console.log(a.hasOwnProperty("constructor"));//false
    console.log(b.hasOwnProperty("constructor"));//false
    console.log(c.hasOwnProperty("constructor"));//false
    console.log(a.constructor);//Function()
    console.log(b.constructor);//String()
    console.log(c.constructor);//Object()

Answer 1

The prototype property is only available on a constructor function. ‘a’ is a function and thus has a prototype. ‘b’ and ‘c’ are instances. They do not have prototypes, their constructors have prototypes:

console.log(a.constructor.hasOwnProperty("prototype")) // true
console.log(b.constructor.hasOwnProperty("prototype")) // true
console.log(c.constructor.hasOwnProperty("prototype")) // true