Detailed explanation of practical ways to create objects and object inheritance in JavaScript_Basic knowledge

Convention in this article: Without special declaration, attributes refer to attributes or methods.

Creating objects and object inheritance are actually the same thing: the instance objects we need obtain private properties through the constructor and shared properties through the prototype chain. What is a good way? Private properties are obtained through the constructor (regardless of custom private properties in the instance) and do not need to be rewritten. Shared properties are found through the prototype chain and do not need to be repeatedly created.

Universal approach

Create objects using a combination of constructor pattern and prototype pattern

function HNU_student(name) {
  this.name = name;
  this.sayName = function() {
    return this.name;
  };
}
HNU_student.prototype = {
  school: 'HNU',
  saySchool: function() {
    return this.school;
  }
};
Object.defineProperty(HNU_student, 'constructor', {value: HNU_student});

var hiyohoo = new HNU_student('xujian');

The prototype will be rewritten through literals, and the constructor of the prototype points to Object. If necessary, the constructor needs to be redefined.

Parasitic Combinatorial Inheritance

function object(o) {
  function F() {};
  F.prototype = o;
  return new F();
}
function inheritPrototype(child, parent) {
  var prototype = object(parent.prototype);
  prototype.constructor = child;
  child.prototype = prototype;
}

function HNU_student(name) {
  this.name = name;
  this.sayName = function() {
    return this.name;
  };
}
HNU_student.prototype.school = 'HNU';
HNU_student.prototype.saySchool = function() {
  return this.school;
};

function Student_2011(name, number) {
  HNU_student.call(this, name);
  this.number = number;
  this.sayNumber = function() {
    return this.number;
  }
}
inheritPrototype(Student_2011, HNU_student);
Student_2011.prototype.graduationTime = 2015;
Student_2011.prototype.sayGraduationTime = function() {
  return this.graduationTime;
};

var hiyohoo = new Student_2011('xujian', 20110803203);

The role of object(): Turn the object passed in as a parameter into the prototype of the instance, and the properties of the object are shared by all instances.

Shared attributes: inheritPrototype(Student_2011, HNU_student);, the sub-constructor prototype becomes an instance of the super-constructor prototype, and the attributes in the super-constructor prototype are shared with the sub-constructor.
Private properties: HNU_student.call(this, name);, when creating an instance through the sub-constructor, call the super-constructor to create private properties.

Other ways to create objects

Dynamic Prototype Mode

function HNU_student(name) {
  this.name = name;
  this.sayName = function() {
    return this.name;
  };

  if (!HNU_student.prototype.school) {
    HNU_student.prototype.school = 'HNU';
    HNU_student.prototype.saySchool = function() {
      return this.school;
    };
  }
}

var hiyohoo = new HNU_student('xujian');

Put the shared properties defined in the prototype into the constructor, use judgment statements, and initialize the prototype shared properties when the constructor is called for the first time to create an instance.

Parasitic Constructor Pattern

function SpecialArray() {
  var values = new Array();
  values.push.apply(values, arguments);
  values.toPipedString = function() {
    return this.join('|');
  };

  return values;
}

var colors = new SpecialArray('red', 'black', 'white');

is used to add special attributes to the native constructor.

Other ways of object inheritance

Combined inheritance

function HNU_student(name) {
  this.name = name;
  this.sayName = function() {
    return this.name;
  };
}
HNU_student.prototype.school = 'HNU';
HNU_student.prototype.saySchool = function() {
  return this.school;
};
function Student_2011(name, number) {
  HNU_student.call(this, name);
  this.number = number;
  this.sayNumber = function() {
    return this.number;
  };
}
Student_2011.prototype = new HNU_student();
Student_2011.prototype.constructor = Student_2011;
Student_2011.prototype.graduationTime = 2015;
Student_2011.prototype.sayGraduationTime = function() {
  return this.graduationTime;
}
var hiyohoo = new Student_2011('xujian', 20110803203);

Shared attributes: Student_2011.prototype = new HNU_student();, the prototype of the sub-constructor points to the prototype of the super-constructor, and the instance finds all shared attributes through the prototype chain.
Private properties: HNU_student.call(this, name);, when creating an instance through the sub-constructor, call the super-constructor to create private properties.

Defect: The super constructor is called twice. Student_2011.prototype = new HNU_student(); at the same time, the private properties defined by the super constructor are created in the sub-constructor prototype. The private properties in these prototypes are overwritten and blocked by the properties of the same name in the instance.

Prototypal inheritance, parasitic inheritance

function object(o) {
  function F() {}
  F.prototype = o;
  return new F();
}
var student1 = {
  school: 'HNU',
  saySchool: function() {
    return this.school;
  }
};
var student2 = object(student1);

Object.creat() is a new method in ECMAScript5. It accepts two parameters: one is the original object as the prototype, and the other is the object that overrides or adds attributes. Its function is the same as the custom object().

var student1 = {
  name: 'xujian',
  school: 'HNU'
};
var student2 = Object.create(student1, {
  name: {
    value: 'huangjing'
  }
});

Parasitic inheritance adds additional attributes to enhance objects based on prototypal inheritance.

function object(o) {
  function F() {}
  F.prototype = o;
  return new F();
}
function creatAnother(original) {
  var clone = object(original);
  clone.sayHi = function() {
    alert('Hi!');
  };
  return clone;
}
var student1 = {
  school: 'HNU',
  saySchool: function() {
    return this.school;
  }
};
var student2 = creatAnother(student1);

Prototypal inheritance and parasitic inheritance are used to create instance objects similar to existing objects.