从子对象调用父母构造函数和原型

Question

I am trying to understand the methods to call constructor and prototype methods in JavaScript.

Here is my try:

function A() {
    this.getId = function() {
        console.log('A constructor - getId');
    }
}
A.prototype.getId = function() {
    console.log('A prototype - getId');
}
function B() {
    A.call(this);
    this.getId = function() {
        console.log('B constructor - getId');
    }
}
B.prototype = Object.create(A.prototype);
B.prototype.constructor = B;

B.prototype.getId = function() {
    console.log('B prototype - getId');
}
var p = new A();
var q = new B();

p.getId()
//A constructor - getId 

q.getId()
//B constructor - getId

p.constructor.prototype.getId()
//A prototype - getId 

q.constructor.prototype.getId()
//B prototype - getId  

Are last two ways are correct way to Call prototype methods?

How can I call parents constructor and prototype methods from child object q?

Answer 1

So, how can I get

'B prototype - getId' from q object

Because q is an instance of B . The B constructor assigns a getId method directly on the instance, so that's the one you get. If you were expecting the one on B.prototype , then you need to remove (or not assign) the one on the instance:

// delete getId on instance
delete q.getId; 

// Now get inherited getId
q.getId()  // B prototype - getId

Note that the delete operator only works on own properties, it won't delete properties on the [[Prototype]] chain.

Are last two ways are correct way to

1. Call parents prototype method using p Parents constructor method using
2. q

"Correct" in that they work, though I wouldn't design it to work that way.