jQuery方法中的奇怪n

Question

我有這個jQuery方法，其中工作正常，如果我在頁面上有元素髮現其中有類.singlePaneOfGlassBlock。

function replaceRightClickIcefacesMethod() { 
     //I only want this to run on IE for now, but the content 
     //is prepared to run on other browsers too 
     if (jQuery.browser.msie) { 
      var elem = jQuery(".singlePaneOfGlassBlock"), oldName = elem 
        .attr("oncontextmenu"), fn = String; 

      //IE returns function instead of string so let's try to take the string 
      //in the right way 
      if (typeof oldName == "function") { 
       oldName = elem[0].getAttributeNode("oncontextmenu").value, 
         fn = Function; 
      } 
      //do the replace 
      oldName = oldName.replace('Ice.Menu.contextMenuPopup', 
        'contextMenuPopupUpdated'); 
      //change oncontextmenu with the new value 
      jQuery.each(elem, function() { 
       this.setAttribute("oncontextmenu", fn(oldName)); 
      }) 
     } 
    } 

但與此錯誤failes：

`'undefined' is null or not an object` 

在哪裏它試圖做的，如果我是其中那些類型元素的缺少其它頁面替換該行...

我已添加一個檢查以查看它是否爲null或者在執行替換之前是否包含該字符串，但仍然失敗：

if (jQuery(oldName).length || oldName.indexOf("Ice.Menu.contextMenuPopup") != -1) { 
     oldName = oldName.replace('Ice.Menu.contextMenuPopup', 
       'contextMenuPopupUpdated'); 
     jQuery.each(elem, function() { 
      this.setAttribute("oncontextmenu", fn(oldName)); 
     }) 
    } 

你能給我一個解決方案嗎？

謝謝。

UPDATE：當我問一個解決方案我只是問如何糾正這種方法不運行時，找不到類型的元素？

Answer 1

更新：重新您在更新後的代碼問題：

function replaceRightClickIcefacesMethod() { 
    if (jQuery.browser.msie) { 
     var elem = jQuery(".singlePaneOfGlassBlock"), oldName = elem 
       .attr("oncontextmenu"), fn = String; 

     if (typeof oldName == "function") { 
      oldName = elem[0].getAttributeNode("oncontextmenu").value, 
        fn = Function; 
     } 

     // ====> This is where the bug is, you're assuming you have 
     //  a string at this point, but you don't necessarily, 
     //  because if there is no match at all, `attr` will 
     //  return `undefined` or `null` (I forget which). 
     //do the replace 
     oldName = oldName.replace('Ice.Menu.contextMenuPopup', 
       'contextMenuPopupUpdated'); 
     //change oncontextmenu with the new value 
     jQuery.each(elem, function() { 
      this.setAttribute("oncontextmenu", fn(oldName)); 
     }) 
    } 
} 

修復：

function replaceRightClickIcefacesMethod() { 
    if (jQuery.browser.msie) { 
     var elem = jQuery(".singlePaneOfGlassBlock"), oldName = elem 
       .attr("oncontextmenu"), fn = String; 

     if (typeof oldName == "function") { 
      oldName = elem[0].getAttributeNode("oncontextmenu").value, 
        fn = Function; 
     } 

     // ====> Add this `if`: 
     if (oldName) { 
      //do the replace 
      oldName = oldName.replace('Ice.Menu.contextMenuPopup', 
        'contextMenuPopupUpdated'); 
      //change oncontextmenu with the new value 
      jQuery.each(elem, function() { 
       this.setAttribute("oncontextmenu", fn(oldName)); 
      }); 
     } 
    } 
} 

---

原來的答覆：

在我看來，你錯過了一些括號（至少）：

function replaceRightClickIcefacesMethod() { 
if (jQuery.browser.msie) { 
    var elem = jQuery(".singlePaneOfGlassBlock"), oldName = elem 
      .attr("oncontextmenu"), fn = String; 
    if (typeof oldName == "function") { // <=== Added { here 
     oldName = elem[0].getAttributeNode("oncontextmenu").value, 
       fn = Function; 

     oldName = oldName.replace('Ice.Menu.contextMenuPopup', 
       'contextMenuPopupUpdated'); 
     jQuery.each(elem, function() { 
      this.setAttribute("oncontextmenu", fn(oldName)); 
     }) 
    } // <=== Added } here 
} 
} 

這裏是上面修正後的縮進：

function replaceRightClickIcefacesMethod() { 
    if (jQuery.browser.msie) { 
     var elem = jQuery(".singlePaneOfGlassBlock"), oldName = elem 
       .attr("oncontextmenu"), fn = String; 
     if (typeof oldName == "function") { // <=== Added { here 
      oldName = elem[0].getAttributeNode("oncontextmenu").value, 
        fn = Function; 

      oldName = oldName.replace('Ice.Menu.contextMenuPopup', 
        'contextMenuPopupUpdated'); 
      jQuery.each(elem, function() { 
       this.setAttribute("oncontextmenu", fn(oldName)); 
      }) 
     } // <=== Added } here 
    } 
} 

這是您的原始與修正的縮進：

function replaceRightClickIcefacesMethod() { 
    if (jQuery.browser.msie) { 
     var elem = jQuery(".singlePaneOfGlassBlock"), oldName = elem 
       .attr("oncontextmenu"), fn = String; 
     if (typeof oldName == "function") 
      oldName = elem[0].getAttributeNode("oncontextmenu").value, 
        fn = Function; 

     // Note how these statements are NOT protected by the `if` 
     // above, and so if `oldName` is `undefined` (as opposed to 
     // being a String or Function. 
     oldName = oldName.replace('Ice.Menu.contextMenuPopup', 
       'contextMenuPopupUpdated'); 
     jQuery.each(elem, function() { 
      this.setAttribute("oncontextmenu", fn(oldName)); 
     }) 
    } 
} 

或者，它可能是你缺少一個else條款並可能進一步防禦if：

function replaceRightClickIcefacesMethod() { 
    if (jQuery.browser.msie) { 
     var elem = jQuery(".singlePaneOfGlassBlock"), oldName = elem 
       .attr("oncontextmenu"), fn = String; 
     if (typeof oldName == "function") { 
      oldName = elem[0].getAttributeNode("oncontextmenu").value, 
        fn = Function; 
     } 
     else {  
      oldName = oldName.replace('Ice.Menu.contextMenuPopup', 
        'contextMenuPopupUpdated'); 
     } 
     if (oldName) { 
      jQuery.each(elem, function() { 
       this.setAttribute("oncontextmenu", fn(oldName)); 
      }); 
     } 
    } 
} 

但它真的很難說，我不能完全遵循的邏輯。它的功能路徑部分似乎沒有改變任何東西，但字符串路徑部分...

Answer 2

而不是jQuery(oldName).length，爲什麼不只是做oldName != null？

Answer 3

Can you give me a solution?

我不確定 - 對於初學者，請格式化您的代碼，以便它更清楚它應該做什麼。它看起來像就像你可能有一對大括號後面的if條件。

至少，不要使用逗號分隔的表達式來實現兩個賦值 - 將該塊放在大括號中並正確拆分兩個賦值。然後代碼邏輯應該變得更清晰。

在任何情況下，因爲當類不存在於頁面上您的問題只發生，這應該是你的第一測試：

function replaceRightClickIcefacesMethod() { 
    if (jQuery.browser.msie) { 
     var elem = jQuery(".singlePaneOfGlassBlock"); 

     if (elem.length > 0) { // new test here! 

      var oldName = elem.attr("oncontextmenu"); 
      var fn = String; 

      if (typeof oldName == "function") { 
       oldName = elem[0].getAttributeNode("oncontextmenu").value; 
       fn = Function; 
      } 

      //do the replace 
      oldName = oldName.replace('Ice.Menu.contextMenuPopup', 
             'contextMenuPopupUpdated'); 

      //change oncontextmenu with the new value 
      jQuery.each(elem, function() { 
       this.setAttribute("oncontextmenu", fn(oldName)); 
      }); 
     } 
    } 
}