javascript - 为什么我在 Javascript 中收到错误消息对象没有方法？

Question

我有以下代码但是我收到错误 Uncaught TypeError: Object #<addThis> has no method 'returnValue' (anonymous function)

function addThis() {
    this.value1 = 1;
    this.value2 = 2;

    var returnValue = function () {
        return (this.value1 + this.value2);
    }
}

//Instantiate object and write response
var simpleObject = new addThis();
document.write(simpleObject.returnValue());

Answer 1

因为 returnValue 只是 addThis 函数中的局部变量，所以它不会在创建的对象中结束。

将函数分配给对象的属性:

function addThis() {
  this.value1 = 1;
  this.value2 = 2;

  this.returnValue = function() {
    return this.value1 + this.value2;
  };
}

或者使用对象的原型(prototype):

function addThis() {
  this.value1 = 1;
  this.value2 = 2;
}

addThis.prototype.returnValue = function() {
  return this.value1 + this.value2;
};