方法错误：未定义方法名称

Question

为什么这段代码不起作用？我正在尝试使用该方法来添加属性，然后将添加的属性分配给它自己的值。

function howLongILivedSomewhere(college, home1, home2) {
    this.birthHome = 18;
    this.college = college;
    this.home1 = home1;
    this.home2 = home2;

    this.calcYearsAlive = function() {
    return birthHome + college + home1 +home2;
    };

    this.yearsAlive = calcYearsAlive();
}

var me = new howLongILivedSomewhere(4, 2, 3);

console.log(me);

Answer 1

您在方法/媒体资源调用期间错过了this关键字。试试如下。

  function howLongILivedSomewhere(college, home1, home2) {
    this.birthHome = 18;
    this.college = college;
    this.home1 = home1;
    this.home2 = home2;

    this.calcYearsAlive = function() {
      return this.birthHome + this.college + this.home1 + this.home2;
    };

    this.yearsAlive = this.calcYearsAlive();
}

var me = new howLongILivedSomewhere(4, 2, 3);

console.log(me.yearsAlive); // output: 27

什么是this关键字？

与其他语言相比，函数的此关键字在JavaScript中的行为略有不同。它在严格模式和非严格模式之间也有一些区别。

<强>参考：
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/this
How does "this" keyword work within a function?

Answer 2

将构造函数更新为：

function howLongILivedSomewhere(college, home1, home2) {
    this.birthHome = 18;
    this.college = college;
    this.home1 = home1;
    this.home2 = home2;

    this.calcYearsAlive = function() {
      return this.birthHome + this.college + this.home1 + this.home2;
    };

    this.yearsAlive = this.calcYearsAlive();
}

var me = new howLongILivedSomewhere(4, 2, 3);

console.log(me);

当您需要访问对象属性时使用this关键字（see here更多详细信息）。