javascript类中的方法链接

Question

I am new in javascript. And I'm trying to figure out how classes work. I have this piece of code:

class TestObject {
  constructor(initialNumber) {
    this.result = initialNumber;
}
  add(number) {
    this.result += number;
    return this;
  }
}

const value = new TestObject(7)
    .add(2)
    .add(3);
console.log(value)

Value returns like this {result: 12} But I need it to be just the integer 12 . Is there any way to fix this by making changes ?

Answer 1

As your value variable is an instance of TestObject , so you can use

console.log(value.result);

 class TestObject { constructor(initialNumber) { this.result = initialNumber; } add(number) { this.result += number; return this; } } const value = new TestObject(7) .add(2) .add(3); console.log(value.result); 

Answer 2

...by making changes only in the class body ?

No. You'd have to change something outside it as well, because your add method returns an object, not a number. So something has to say "I want a number instead please."

If you add a valueOf method to your class:

valueOf() {
    return this.result;
}

...then the thing outside the class body could be just a + :

console.log(+value);

...but that's still outside the class body.

Live example:

 class TestObject { constructor(initialNumber) { this.result = initialNumber; } add(number) { this.result += number; return this; } valueOf() { return this.result; } } const value = new TestObject(7) .add(2) .add(3); console.log(+value); 

Answer 3

This is happening because you returning the result from your method so the value will be a object {result:12} , If you want to see the execution and debug it, please add debugger; to any line you need you can understand what is getting;

    class TestObject {
      constructor(initialNumber) {
        this.result = initialNumber;
    }
      add(number) {
        this.result += number;
        debugger;
        return this;
      }
    }

    const value = new TestObject(7)
        .add(2)
        .add(3);
     debugger;
    console.log(value)

with the code what you wrote, if you change the Console.log(value.result) you will get the desired result .