函數內部的javascript類變量表示未定義的ES6

Question

class Auto {
  printauto() {
    var type = "2 wheeler";
    var color = "green";
    console.log("Car type is="+this.type+" "+" and color="+this.color);
 }
}

var a = new Auto();
a.printauto();

為什么輸出未定義？

汽車類型=未定義且顏色=未定義

Answer 1

僅通過聲明將變量附加到類上下文不會發生。 你必須明確：

 class Auto { printauto() { this.type = "2 wheeler"; // explicitly attach to `this` this.color = "green"; // same here console.log("Car type is="+this.type+" "+" and color="+this.color); } } new Auto().printauto(); 

構造函數通常是進行此類初始化的最佳位置：

 class Auto { constructor() { this.type = "2 wheeler"; // explicitly attach to `this` this.color = "green"; // same here } printauto() { console.log("Car type is="+this.type+" "+" and color="+this.color); } } new Auto().printauto(); 

Answer 2

這是指類，您沒有在類中聲明顏色和類型。 顏色並在您的printauto方法范圍內。 要么在課堂上宣布它們，要么就是這樣做

console.log("Car type is="+type+" "+" and color="+color);

通過在課堂上宣布

class Auto {
    this.type = "2 wheeler";
    this.color = "green";

    printauto() {
        console.log("Car type is=" + this.type + " " + " and color=" + this.color);
    }
}
var a = new Auto();
a.printauto();

Answer 3

正如Felix King在評論中所描述的，變量a與Auto類的屬性不同

 class Auto { printauto() { var type = "2 wheeler"; var color = "green"; console.log("Car type is="+ type+" "+" and color="+color); } } var a = new Auto(); a.printauto();