Compatibility process removes events

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Document</title>
</head>
<body>
  <input type="button" value="按钮" id="btn">
  <script src="common.js"></script>
  <=btnwas>script
     my$('btn');
    function btnClick() {
      alert('hello');
      // 移除事件
      removeEventListener(btn, 'click', btnClick);
    }
    addEventListener(btn, 'click', btnClick);
  </script>
</body>
</html>

common codes

function My $ (ID) {
   return document.getElementById (ID); 
} 

// process browser compatibility 
// Get first child 
function getFirstElementChild (Element) {
     var Node, Nodes = the element.childNodes, I = 0 ;
     the while (Node = Nodes [I ++ ]) {
         IF (node.nodeType ===. 1 ) {
             return Node; 
        } 
    } 
    return  null ; 
} 

// process browser compatibility 
// Get the next sibling 
 function getNextElementSibling (element) {
     var EL =Element;
     the while (EL = el.nextSibling) {
       IF (el.nodeType ===. 1 ) {
           return EL; 
      } 
    } 
    return  null ; 
  } 


// compatibility problems and processing innerText textContent of 
// the content between the tags set 
function setInnerText (Element, Content) {
   // determines whether the current browser support the innerText 
  iF ( typeof element.innerText === 'String' ) { 
    element.innerText = Content; 
  } the else { 
    element.textContent = Content;  
  }
}

// compatibility issues deal with registered events 
// eventName, without ON, the Click mouseOver mouseout 
function addEventListener (Element, eventName, the Fn) {
   // determine whether the current browser supports addEventListener method 
  IF (element.addEventListener) { 
    element.addEventListener (eventName, Fn);   // third parameter defaults to false 
  } the else  IF (element.attachEvent) { 
    element.attachEvent ( 'ON' + eventName, Fn); 
  } the else {
     // corresponds element.onclick = fn; 
    Element [ 'ON' eventName +] = Fn; 
  } 
} 

// process removes compatibility event handling
function the removeEventListener (Element, eventName, Fn) {
   IF (element.removeEventListener) { 
    element.removeEventListener (eventName, Fn); 
  } the else  IF (element.detachEvent) { 
    element.detachEvent ( 'ON' + eventName, Fn); 
  } the else { 
    Element [ 'ON' eventName +] = null ; 
  } 
} 

// Get browser compatibility issues page scrolling distance 
// Get out from the page scrolling 
function getScroll () {
   var the scrollLeft = || document.body.scrollLeft Document .documentElement.scrollLeft;
   var= || document.body.scrollTop scrollTopdocument.documentElement.scrollTop;
   return { 
    the scrollLeft: the scrollLeft, 
    scrollTop: scrollTop 
  } 
} 

// Get the mouse position on the page, the browser compatibility processing 
function the getPage (E) {
   var the pageX e.clientX || + = e.pageX getScroll () .scrollLeft;
   var pageY e.clientY || + = e.pageY getScroll () scrollTop;.
   return { 
    the pageX: the pageX, 
    pageY: pageY 
  } 
}

Compatibility process removes events

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