Javascript：从对象中查找值

Question

I have the following object:

var stuff = {}; 
stuff["jar"] = "biscuit"; 
stuff["cupboard"] = "food"; 

Iterating through the list with an For i loop and getting the value is easy, but how would I get the key?

for (var i in stuff) {  
    var key = GET KEY SOMEHOW 
    var val = stuff[i];   
}  

Answer 1

The key is i . However, make sure that the key is in your object, not part of the prototype chain.

for (var i in stuff) {
  var key = i;
  if (stuff.hasOwnProperty(i)) {
    var val = stuff[i];   
  }
}  

See also:

• https://developer.mozilla.org/en/JavaScript/Reference/Statements/for...in
• https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Object/hasOwnProperty

Answer 2

var key = i;

在Javascript的for (foo in bar)如果foo是对象或数组的索引并且恰好是字符串，则在调用foo时应打印或分配该字符串。

Answer 3

You already have it:

for (var key in stuff) {
    var val = stuff[key];
}

Answer 4

If you have the value already you may find the key by using this logic :

for (var i=0;i<numKeyValuePairs;i++)
{
if(val==key[i])
{
document.write(key[i];
}
}