如何获取JavaScript对象的最后一项?

2021年3月13日15:23:50 发表评论 395 次浏览

给定一个JavaScript对象, 任务是获取JavaScript对象的最后一个元素。

方法1:

  • 采用Object.keys()方法获取对象的所有键。
  • 现在, 使用索引来访问JavaScript对象的最后一个元素。

例子:本示例实现了上述方法。

<!DOCTYPE HTML> 
< html > 
  
< head > 
     < title > 
         How to get the last item
         of JavaScript object ?
     </ title >     
</ head > 
  
< body style = "text-align:center;" > 
      
     < h1 style = "color:green;" > 
         lsbin 
     </ h1 > 
      
     < p id = "GFG_UP1" style = 
         "font-size: 15px; font-weight: bold;" > 
     </ p > 
      
     < p id = "GFG_UP2" style = "font-size: 15px;
             font-weight: bold; color: green;"> 
     </ p > 
      
     < button onclick = "GFG_Fun()" > 
         click here 
     </ button > 
      
     < p id = "GFG_DOWN" style = "color:green;
         font-size: 20px; font-weight: bold;"> 
     </ p >
      
     < script > 
         var up1 = document.getElementById('GFG_UP1'); 
         var up2 = document.getElementById('GFG_UP2'); 
         var down = document.getElementById('GFG_DOWN'); 
          
         var Obj = { 
             "1_prop": "1_Val", "2_prop": "2_Val", "3_prop": "3_Val" 
         }; 
          
         up1.innerHTML = "Click on the button to get"
                 + "the last element of the Object."; 
          
         up2.innerHTML = JSON.stringify(Obj); 
          
         function GFG_Fun() { 
             down.innerHTML = "The last key = '" + 
                 Object.keys(Obj)[Object.keys(Obj).length-1]
                 + "' < br > Value = '" 
                 + Obj[Object.keys(Obj)[Object.keys(Obj).length-1]]
                 + "'"; 
         } 
     </ script > 
</ body > 
  
</ html >

输出如下:

在单击按钮之前:

如何获取JavaScript对象的最后一项?1

单击按钮后:

如何获取JavaScript对象的最后一项?2

方法二:

  • 采用for循环要访问对象的所有键, 则在循环结束时, 循环变量将具有对象的最后一个键。
  • 现在, 使用索引来访问JavaScript对象的最后一个元素的值。

例子:本示例实现了上述方法。

<!DOCTYPE HTML> 
< html > 
  
< head > 
     < title > 
         How to get the last item
         of JavaScript object ?
     </ title >     
</ head > 
  
< body style = "text-align:center;" > 
      
     < h1 style = "color:green;" > 
         lsbin 
     </ h1 > 
      
     < p id = "GFG_UP1" style = 
         "font-size: 15px; font-weight: bold;" > 
     </ p > 
      
     < p id = "GFG_UP2" style = "font-size: 15px;
         font-weight: bold; color: green;"> 
     </ p >
      
     < button onclick = "GFG_Fun()" > 
         click here 
     </ button > 
      
     < p id = "GFG_DOWN" style = "color:green;
         font-size: 20px; font-weight: bold;"> 
     </ p >
      
     < script > 
         var up1 = document.getElementById('GFG_UP1'); 
         var up2 = document.getElementById('GFG_UP2'); 
         var down = document.getElementById('GFG_DOWN'); 
          
         var Obj = { 
             "1_prop": "1_Val", "2_prop": "2_Val", "3_prop": "3_Val" 
         }; 
          
         up1.innerHTML = "Click on the button to get"
                 + "the last element of the Object."; 
          
         up2.innerHTML = JSON.stringify(Obj); 
          
         function GFG_Fun() {
             var lastElement;
              
             for (lastElement in Obj);
                 lastElement;
              
             down.innerHTML = "The last key = '" + 
                 lastElement + "' < br > Value = '" 
                 + Obj[lastElement] + "'"; 
         } 
     </ script > 
</ body > 
  
</ html >

输出如下:

在单击按钮之前:

如何获取JavaScript对象的最后一项?3

单击按钮后:

如何获取JavaScript对象的最后一项?4

木子山

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