How to access a method from a class from another c

问题:

I want to use Object Oriented Programming technique with JavaScript but I can't access a method from one class from another class. How can do like the following?

class one{

  write(){
    console.log("Yes! I did!");
  }
}

class two{
   var object=new one();

   tryingMethod(){
   object.write();
   }
}

I get the following error:

Uncaught SyntaxError: Unexpected identifier -->> for var object=new one();

回答1:

Your syntax is not legal. There should be an error in your console showing you which line of code is not correct.

If it's a static method (doesn't use any instance data), then declare it as a static method and you can directly call it.

If it's an instance method, then you would typically create an object of type one and then call the method on that object (usually in the constructor).

To make the method static (which appears to be fine in your specific case):

class One {
  static write(){
    console.log("Yes! I did!");
  }
}

class Two {
   tryingMethod(){
     One.write();
   }
}

For the non-static case, you don't have the proper syntax. It appears you want to create the instance of the One object in a constructor for Two like this:

class One {
  write(){
    console.log("Yes! I did!");
  }
}

class Two {
   constructor() {
       this.one = new One();
   }

   tryingMethod(){
     this.one.write();
   }
}

var x = new Two();
x.tryingMethod();

Note: I'm also following a common Javascript convention of using an identifier that starts with a capital letter for the class/constructor name such as One instead of one.

回答2:

What I'd recommend doing is not tying the classes together so tightly and doing something like this...

class One {
  write() {
    console.log("Yes! I did!");
  }
}

class Two {
  constructor(one = new One())  {
    this.one = one;
  }
  tryingMethod() {
    this.one.write();
  }
}

Now what you can do is...

const two = new Two();
two.write();

This allows you to have a better separation of concerns and allows you to more easily unit test the Two class because you can pass in a mock implementation of the One class if you want.

describe("two class", () => {
  it("should do something", () => {
    const one = {
      write: sinon.spy()
    };
    const two = new Two(one)

    two.tryingMethod();

    expect(one.write.calledOnce).to.be.ok;
  });
});