属性在我的自定义构造函数中不能正常工作- Javascript

Question

我试图在Javascript中创建一个自定义构造函数，但我似乎无法理解为什么控制台不记录"Investigating"的'Letters'属性，该属性是由构造函数“谓词”创建的：

function Verb (tense, transitivity) {
    this.tense = tense;
    this.transitivity = transitivity;
    **this.letter1 = this.charAt(0);
    this.letter2 = this.charAt(2);
    this.letter3 = this.charAt(4);
    this.Letters = this.letter1 + " " + this.letter2 + " " + this.letter3;**

}

var Investigating = new Verb ("present", "transitive");


console.log(Investigating.tense);  // present
**console.log(Investigating.Letters); //console doesn't log anything**

我在这里做错什么了？会很感激你们的帮助，谢谢。

Answer 1

在构造函数中，this指的是正在创建的obj，.so this.charAt(0) is incorrect.since对象在其原型链中没有charAt方法。(字符串和数组有此方法).i认为您正在尝试这样做。

this.letter1 = this.transitivity.charAt(0);
this.letter2 = this.transitivity.charAt(2);
this.letter3 = this.transitivity.charAt(4);
this.Letters = this.letter1 + " " + this.letter2 + " " + this.letter3;`