通过自定义类javascript的元素获取自定义类

如何访问主要城市元素和城市的另一个元素

您的问题是

警报（this.city）

中的

此

实际上指的是

此.circle

单击的元素-因此您需要在函数中控制

此

引用。这里有三种方法：

使用

function city(circle,reinf)
        {
            this.reinf = reinf;
            this.circle.onmouseover = function(){
                alert(this.city);
            }   
        }

使用

功能城市（圆形，reinf）{
this.city=“Foo”；
这个圆=圆；
this.reinf=reinf；
this.circle.onmouseinter=（）=>{//
function city(circle, reinf) {

    this.city = "Foo";
    this.circle = circle; // Forgot this one?
    this.reinf = reinf;

    this.circle.onmouseenter = function(){
        alert(this.city);
    }.bind(this);   // << bind to the outer this context
}

function city(circle, reinf) {
    var self = this;

    this.city = "Foo";
    this.circle = circle;
    this.reinf = reinf;

    this.circle.onmouseenter = function(){
        alert(self.city);   // << refer to self
    }
}

function city(circle, reinf) {

    this.city = "Foo";
    this.circle = circle;
    this.reinf = reinf;

    this.circle.onmouseenter = () => { // << Arrow function with unbound this 
        alert(this.city);
    };
}