不能實例

Question

內閱讀對象屬性（不確定？）當我試圖從事件功能onMouveMove我得到以下錯誤訪問對象this.guy：

"Uncaught TypeError: Cannot read property 'prop1' of undefined" 

當我檢查Chrome的Devtool，價值存在並存在，它只是無法識別「onMouseMove」功能。

MyClass = function(some_html_element){ 
 
    this.guy = {"prop1":[]}; 
 
    some_html_element.onmousemove = this.onMouseMove; 
 
} 
 
    
 
MyClass.prototype.onMouseMove = function(evt){ 
 
    if(!this.guy.prop1){ //<- here's the error 
 
      alert("no error"); 
 
    } 
 
} 
 

 
a = new MyClass(document.querySelector("#example"))

<div id="example"> 
 
MOVE MOUSE ON ME 
 
</div>

任何想法？

Answer 1

當您爲some_html_element設置onMouseMove處理程序時，該函數未綁定到您的MyClass實例。你可以明確地結合它解決這個問題：

MyClass = function(some_html_element){ 
    this.guy = {"prop1":[]}; 
    some_html_element.onmousemove = this.onMouseMove.bind(this); 
}