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Prototype inheritance


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Kautkā neizdodas uztvert JS prototype inheritance mehānismu. 

Gribu realizēt mantošanu 3 līmeņos (piemēram)

var A=function(paramsA) {
    this.paramsA=paramsA;
    this.init();
};

A.prototype={
    paramsA:null,
    init: function() {
        console.log(this.paramsA);
    },
};

var B=function(paramsB, paramsA) {
    this.prototype=Object.create(A, {paramsA: { writable: true, configurable: true, value: paramsA },})
    this.paramsB=paramsB;
};

B.prototype={
    paramsB: null,
    click: function() {
        console.log(this.paramsB);
    }
};

var C=function(paramsC, paramsB, paramsA) {
    this.prototype=Object.create(C, {
        paramsA: { writable: true, configurable: true, value: paramsA },
        paramsB: { writable: true, configurable: true, value: paramsB },
    })
    this.paramsC=paramsC;
};

C.prototype={
    paramsC: null,
    render: function() {
        console.log(this.paramsC);
    },
};

var Obj=new C(1,2,3); //console.log => 3
Obj.render(); //console.log => 1
Obj.click(); //console.log => 2

Vēlamais output konsolē:

3
1
2

Sobrīd dabūju konsolē:

1
Obj.click is not a function

Nevaru saprast īsti kā realizēt šādu inheritance JS vidē. 

 

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8 answers to this question

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Pa manam, izskatās, ka tu vienkārši pārraksti visu prototipa objektu pa virsu. Bet principā vajadzētu pārrakstīt tikai to, kas mainās, ko vēlies overraidot.

x.proto = {};
x.proto.a = 1;

x.proto = { b: 2}; // Šeit taču pazūd iepriekšējais {a:1}, jo vienkārši pārraksti.
vs
x.proto.b = 2; // Šajā gadījumā tu pievieno jaunu metodi, vecā paliek.

Varbūt kļūdos. Nekad īsti neesmu vairāk par 1 līmeni manotjis prototipus.

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Tā izskatās, prātu man sačakarē arī tas, ka katram objektam ir vajadzīgs konstruktors, un to definē kā funkciju (cik sparotu), savukārt paša objekta body ir kā funkcijas prototips. Rezultātā man vajadzīgs lai protopips extendojas no cita prototipa. Varbūt kautkas pašā būtībā ir galīgi šķersām. 

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var A = function (paramsA)
{
	this.paramsA = paramsA;
	this.init();
};

A.prototype = {
	paramsA: undefined,
	init: function ()
	{
		console.log(this.paramsA);
	}
};

var B = function (paramsB, paramsA)
{
	A.call(this, paramsA);
	this.paramsB = paramsB;
};

B.prototype = Object.create(A.prototype, {
	paramsB: {
		writable: true,
		configurable: true,
		enumerable: true,
		value: undefined
	},
	click: {
		// not writable/configurable/enumerable
		value: function ()
		{
			console.log(this.paramsB);
		}
	}
});
B.prototype.constructor = B;

var C = function (paramsC, paramsB, paramsA)
{
	B.call(this, paramsB, paramsA);
	this.paramsC = paramsC;
};

C.prototype = Object.create(B.prototype, {
	paramsC: {
		writable: true,
		configurable: true,
		enumerable: true,
		value: undefined
	},
	render: {
		// not writable/configurable/enumerable
		value: function ()
		{
			console.log(this.paramsC);
		}
	}
});
C.prototype.constructor = C;

var obj = new C(3, 2, 1); //console.log => 1
obj.click(); //console.log => 2
obj.render(); //console.log => 3

Sources:

https://developer.mozilla.org/en/docs/Web/JavaScript/Inheritance_and_the_prototype_chain

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/create

https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperty- writable/configurable/enumerable explanations

Edited by jurchiks
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