Question

我使用javascript地图来存储键和值。稍后我会检查地图中是否存在指定的键，但它有时会给出正确的结果，但有时却没有。我尝试使用console.log(mapname)打印地图，它显示所有键，但如果我尝试检查是否存在某个指定的键 - 有时它会给出错误的答案。

使用以下代码：

// following code is called n times in loop with different/same vales of x
myMap : new Object();
var key = x  ; // populated dynamically actually
myMap[key] = "dummyval";
if(myIdMap[document.getElementById("abc").value.trim()] != null)
    alert('present');
else
    alert('not present');

可能出现什么问题？ alphanumericstring / integers值可以用作键吗？

Answer 1

var myMap = {};
// ...

//simulating your inner loop; is this close enough?
//Note: A MacGuffin is a plot device to move the story forward. 
//  Like a time machine, or a space ship.
for (var key in macGuffin) { 
    myMap[key] = macGuffin.processItem(key);
}

// ... 
var myKey = document.getElementById("abc").value.trim();
//Note the use of !==; false == null == 0 == '', but null only === null
if (myMap[myKey]!==null)  
//Better?  (typeof myMap[myKey] != 'undefined')
    console.log('present');
else
    console.log('not present');

Answer 2

请确保您知道使用密钥存储的值可能为null，如下面的代码所示：

a = {
   "mykey": null
}

for (x in a) {
   if (a[x] == null) {
      alert(x + " is null!");
   }
} // produces a single alert: "mykey is null!"

Answer 3

我认为您必须将密钥存储在某些临时表或会话或cookie等对象中以供将来检索。你已经在mymap [key]中动态存储x位置值，但每次加载并覆盖你的新值。你那里做错了..

javascript map / object的奇怪行为

3 个答案: