Javascript 获取关联数组的键
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Get key of associative array
提问by Asai Lopze
Hi i'm currently fetching an array with .each
嗨，我目前正在使用 .each 获取一个数组
$.each(messages, function(key,message){ doStuff(); });
But the key is the index of the array and not the associative key.
但是键是数组的索引而不是关联键。
How can I get it easily?
我怎样才能轻松获得它？
Thanks
谢谢
回答by Rocket Hazmat
JavaScript doesn't have "associative arrays". It has arrays:
JavaScript 没有“关联数组”。它有数组：
[1, 2, 3, 4, 5]
and objects:
和对象：
{a: 1, b: 2, c: 3, d: 4, e: 5}
Array's don't have "keys", they have indices, which are counted starting at 0.
数组没有“键”，它们有索引，从 0 开始计数。
Arrays are accessed using [], and objects can be accessed using []or ..
使用 访问数组[]，使用[]或访问对象.。
Example:
例子：
var array = [1,2,3];
array[1] = 4;
console.log(array); // [1,4,3]
var obj = {};
obj.test = 16;
obj['123'] = 24;
console.log(obj); // {test: 16, 123: 24}
If you try to access an array using a string as a key instead of an int, that may cause problems. You would be setting a property of the array and not a value.
如果您尝试使用字符串而不是 int 作为键来访问数组，则可能会导致问题。您将设置数组的属性而不是值。
var array = [1,2,3];
array['test'] = 4; // this doesn't set a value in the array
console.log(array); // [1,2,3]
console.log(array.test); // 4
jQuery's $.eachworks with both of these. In the callback for $.each, the 1st param, key, is either the object's key, or the array's index.
jQuery$.each可以处理这两种情况。在 的回调中$.each，第一个参数key是对象的键或数组的索引。
$.each([1, 2, 3, 4, 5], function(key, value){
console.log(key); // logs 0 1 2 3 4
});
$.each({a: 1, b: 2, c: 3, d: 4, e: 5}, function(key, value){
console.log(key); // logs 'a' 'b' 'c' 'd' 'e'
});
回答by Nishu Tayal
回答by Sune Rasmussen
JavaScript doesn't have "associative arrays" as in PHP, but objects. Objects, though, may have string keys that corresponds to a value. Arrays are lists of values indexed numerically, so, if keyis a number, it must be an array you are working with and not an object, and therefore you cannot get the key, as there is none.
JavaScript 没有 PHP 中的“关联数组”，而是对象。但是，对象可能具有与值对应的字符串键。数组是按数字索引的值列表，因此，如果key是数字，则它必须是您正在使用的数组而不是对象，因此您无法获取键，因为没有键。
Thus, you'd probably want to iterate over an array with a simple for-loop instead of a callback-based iterator such as $.each.
因此，您可能希望使用简单的for-loop 而不是基于回调的迭代器（例如$.each.
