JS elevation 6. Object-oriented Programming (2) Problems in creating objects _3 constructors

# The last time we talked about creating objects with the constructor's schema, we solved the problem of object recognition relative to Factory mode.

1 functionPerson (name,age,job) {2       This. name=name;3       This. age=Age ;4       This. job=job;5       This. sayname=function(){6Console.log ( This. Name);7      }8  }9 Ten  varperson1=NewPerson ("Xiaoming", "Doctor"); OnePerson1.sayname ();//xiaoming

# as above, it is the form of creating objects using the constructor pattern. The main problem with constructors is that each method is recreated on each instance . In fact, the quality can be equivalent to the following forms:

1 functionPerson (name,age,job) {2       This. name=name;3       This. age=Age ;4       This. job=job;5       This. sayname= new Function("Console.log (this.name)");6  }7 8  varperson1=NewPerson ("xiaoming1", "Doctor");9  varPerson2=NewPerson ("Xiaoming2", "Doctor");TenPerson1.sayname ();//xiaoming1 OnePerson2.sayname ();//xiaoming2

# from the above code, although Person1 and Person2 have a sayname method, but in fact two are different function instances. As follows:

1 console.log (person1.sayname==person2.sayname); // false

# This way, when we create many instance objects, it's the equivalent of creating a lot of different sayname () methods that do the same task at the same time, which is obviously not very good!

# Try moving the function definition outside the constructor, as follows:

1 functionPerson (name,age,job) {2       This. name=name;3       This. age=Age ;4       This. job=job;5       This. sayname=Sayname;6  }7 functionSayname () {8Console.log ( This. Name);9 }Ten  varperson1=NewPerson ("xiaoming1", "Doctor"); One  varPerson2=NewPerson ("Xiaoming2", "Doctor"); APerson1.sayname ();//xiaoming1 -Person2.sayname ();//xiaoming2 -  theConsole.log (Person1.sayname==person2.sayname);//true

# as above, it solves the problem that multiple functions do the same function, Person1 and Person2 actually share the Sayname function in the global scope.

# But there are the following issues:

(1) The Sayname function defined in the global scope is actually called by the person object, which makes the global scope a bit of a misnomer.

(2) If you need to define many methods in an object, it means that you need to define many global functions.

(3) The person this custom object type has no encapsulation to speak of.

~ ~ can solve the above problem through the prototype mode.

JS elevation 6. Object-oriented Programming (2) Problems in creating objects _3 constructors