CODEWITHSUNDEEP
javascript
St.Antario
St.Antario

Reputation: 27375

Prototype property of function

Let we have the following JS code:

function doThis(){
    myKeys=[];
    var span= document.createElement("span");
    var parent=document.getElementById("parent");
    var child=document.getElementById("child");
    var submit=document.getElementById("submit");
    child.insertBefore(span,submit.nextSibling);
    Person.prototype={pr: "pr"};
    var p= new Person("Ivan", "Ivanov");
    myKeys.push(getAllKeyValuePair(Person));
    span.innerHTML=myKeys;
}
function getAllKeyValuePair(obj){
    var str="";
    for(var key in obj){
        try{
            str=str+"{"+key+", "+obj[key]+"}";
        }
        catch(e){
            console.log(key);
        }
    }
    return str;
}
function Person(name,surname){
    this.name=name;
    this.surname=surname;
}

JSFIDDLE we declare prototype property of Person constructor function at the line 

Person.prototype={pr: "pr"};

But when I'm trying to print all property of Person I'm excepted that we have at least prototype properties which indicate to {pr: "pr"} object. But if we replace line 

myKeys.push(getAllKeyValuePair(Person));

to the line

myKeys.push(getAllKeyValuePair(Person.prototype));

we can see the {pr, "pr"}. I don't understand this, please explain me why it's occurring?

Upvotes: 2

Views: 71

Answers (1)

apsillers
apsillers

Reputation: 115920

getAllKeyValuePair(Person) asks for all the keys on the Person constructor function. Person.prototype properties are made available to instances that have been built by the constructor:

var p= new Person("Ivan", "Ivanov");
myKeys.push(getAllKeyValuePair(p));

The reason you don't see prototype when you ask for the properties of Person is that prototype is a non-enumerable property. You can see this with:

> Object.getOwnPropertyDescriptor(Person, "prototype");
  > Object {
        value: Object,
        writeable: true,
        enumerable: false,
        configurable: false
    }

If you want to enumerate over all of an object's own properties, use Object.getOwnPropertyNames(Person). Note that this does not capture properties inherited from the object's prototype chain (thus, we say the object's "own" properties, rather than inherited properties).

Upvotes: 3

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