属性在我的自定义构造函数中无法正常运行 - Javascript

Question

我正在尝试在 Javascript 中创建自定义构造函数，但我似乎不明白为什么控制台不会记录 'Letters' "Investigating" 的属性由构造函数创建 "Verb":

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**

我在这里做错了什么？非常感谢你们的帮助，谢谢。

Answer 1

在构造函数中 this 指的是正在创建的对象。所以 this.charAt(0) 是 incorrect.since Object 对象在其原型链中没有 charAt 方法。（字符串和数组有这个方法）。我想你正在尝试做。

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;`

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