工厂功能：为什么状态变量没有变为“OK”？

Question

我正在从 javascript 类切换到工厂函数。 除了参数，我还需要内部属性，例如。以下简化示例中的状态。那么，为什么 status 没有设置为 OK，应该如何设置呢？

const Model = (name) => {
    name = "myname";
    let status = "initial";

    const setOK = () => {
        status = "OK";
    }
    return {name, status, setOK}
};

const m = Model();
console.log(m.status); //status is initial
m.setOK();
console.log(m.status);  //expecting OK, but still initial

Answer 1

目前，返回的对象永远不会改变：你的

return {name, status, setOK}

返回具有这三个属性的对象，其值与返回对象时的值相同。如果您希望对象更改，请在 Model 内预先定义对象，然后在 setOK 内更改所述对象：

const Model = (name) => {
  name = "myname";
  let status = "initial";
  const setOK = () => {
    obj.status = "OK";
  };
  const obj = { name, status, setOK };
  return obj;
};

const m = Model();
console.log(m.status);
m.setOK();
console.log(m.status);

Answer 2

Object Composition

使用Object.assign() 合并对象或“继承” 方法，而不使用class 或prototype。 Composition over inheritance

---

演示

demo中评论的详细信息

/* 
Object monitor has setOK() method. 
Note the parenthesis wrapped around the curly braces ensures
that the object literal will be invoked as a expression.
The props object from Model is passed to monitor object
*/
const monitor = props => ({
  setOK: () => {
    props.status = "OK";
  }
});

/* Factory Function 
Note the object literal props. props will be passed through
Object.assign() method in order to inherit the method setOK() from the monitor object.
*/
const Model = name => {
  let props = {
    name: name,
    status: "initial"
  };
  return Object.assign(props, monitor(props));
};

// Create object m with the name: "checkStatus"
const m = Model("checkStatus");
// Verify object m is named "checkStatus"
console.log('name: '+m.name);
// Check status
console.log('status: '+m.status);
// Invoke .setOK() method
m.setOK();
// Check status
console.log('status: '+m.status);