Reputation: 131
I'm reading You Don't Know JS, and confuse getPrototypeOf and isProtytypeOfs' result. Code like below:
<html>
<script>
function Foo(name) {
this.name = name;
};
Foo.prototype.myName = function() {
return this.name;
};
function Bar(name, label) {
Foo.call(this, name);
this.label = label;
};
Bar.prototype = Object.create(Foo.prototype);
Bar.prototype.myLabel = function() {
return this.label;
};
var a = new Bar("a", "obj a");
console.log("getPrototypeOf:", Object.getPrototypeOf(a));
console.log("Foo.prototype.isPrototypeOf(a):", Foo.prototype.isPrototypeOf(a));
console.log("Object.getPrototypeOf(a) === Foo.prototype:", Object.getPrototypeOf(a) === Foo.prototype);
console.log("Bar.prototype.isPrototypeOf(a):", Bar.prototype.isPrototypeOf(a));
console.log("Object.getPrototypeOf(a) === Bar.prototype:", Object.getPrototypeOf(a) === Bar.prototype);
</script>
The result like below(chrome 64):
getPrototypeOf: Foo {myLabel: ƒ}
Foo.prototype.isPrototypeOf(a): true
Object.getPrototypeOf(a) === Foo.prototype: false
Bar.prototype.isPrototypeOf(a): true
Object.getPrototypeOf(a) === Bar.prototype: true
Why the Foo.prototype.isPrototypeOf(a) is true but "Object.getPrototypeOf(a) === Foo.prototype" is false?
Upvotes: 0
Views: 191
Reputation: 5369
logic is here:
console.log(a instanceof Bar);//true
console.log(Object.getPrototypeOf(a));//Foo { myLabel: [Function] }
console.log(Object.getPrototypeOf(a) instanceof Foo);//true
console.log(Object.getPrototypeOf(Object.getPrototypeOf(a))===Foo.prototype);//true
actually,you can change the code :
Bar.prototype = Object.create(Foo.prototype);
to
Bar.prototype = new Foo();
the result is still the same.May it will be easier to understand though there is a little different between two ways.
just as @Bergi said, Foo.prototype is just in the a's prototype chain but not the "Direct" prototype.
Upvotes: 1