由定制类的元素得到自定义类的JavaScript

Question

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

如何进入主城的元素和城市的另一个元素

Answer 1

你的问题是，在alert(this.city)this实际上指的是this.circle点击的元素 - 因此你需要在您的功能中控制this参考。这里有三种方式：

使用.bind(this)

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 
} 

在可变

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 
    } 
} 

存储this使用Arrow function

function city(circle, reinf) { 

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

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

PS：你也可能不想使用mouseover - 因为它的工作方式与mouseenter完全不同。