获取对象中的下一个键值对 [英] Get next key-value pair in an object

问题描述

给定一个键，我想找到一个对象中的下一个属性。我不能依靠按键来排序或顺序（他们是uuids）。请参考下面的例子：

  var db = {
a：1，
b ：2，
c：3 
} 
 
 var next = function（db，key）{
 // 
} 
 
 next（db，'a'）; //我想要2 
 next（db，'b'）; //我想要一个prev（）函数，但我敢肯定，它会是一个简单的函数。是相同的解决方案。
 
 
 
这似乎是一个微不足道的问题，但我不能为我的生活弄清楚如何做。
 
 
 
对于使用underscore.js的解决方案或写在coffeescript中的解决方法很高兴）。
解决方案
正确的答案是：您不能这样做，因为对象是无序的，如ECMAScript的规范。
 
 
 
我建议您使用有序结构（如数组）来解决问题：
  var db = [
 {key：'a'，value：1}，
 {key：'b'，value：2 }，
 {key：'c'，value：3} 
]; 
  
然后下一个 ：
  var next = function（db，key）{
 for（var i = 0; i  if（db [i] .key === key）{
 return db [i + 1]&& db [i + 1] .value; 
} 
} 
}; 
  
如果键 code> db 或它是最后一个， next 返回 undefined 。如果你永远不会要求下一个最后一个项目，你可以通过删除三元&& 运算符并返回 db [i + 1] .value 。
 
 
 
 c> next 更简单：
  var next = function（db，key）{
 var i = _.pluck（db，'key'）。indexOf（key）; 
 return i！== -1&&& db [i + 1]&& db [i + 1] .value; 
}; 
  
（在这种情况下 next  code> false 有时...但它仍然是一个假值：））
 
 
 
 
 
 
现在，一个更务实的答案可能是，因为大多数浏览器会尊重一个对象在迭代时初始化的顺序，你可以使用在循环，因为其他答案建议。我建议使用  Object.keys  来简化迭代数组的工作：
  //假设db是一个对象在问题中定义。 
 var next = function（db，key）{
 var keys = Object.keys（db）
，i = keys.indexOf（key） 
 return i！== -1&&&键[i + 1]&& db [keys [i + 1]]; 
}; 
  
 
Given a key, I want to find the next property in an object. I can not rely on the keys to be ordered or sequential (they're uuids). Please see below for trivial example of what I want:
var db = {
  a: 1,
  b: 2,
  c: 3
}

var next = function(db, key) {
  // ???
}

next(db, 'a');  // I want 2
next(db, 'b');  // I want 3
I also want a prev() function, but I'm sure it will be the same solution.

This seems like such a trivial problem but I can't for the life of me figure out how to do it.

Happy for the solution to use underscore.js or be written in coffeescript :)
解决方案
The correct answer is: you can't do that, as objects are unordered as per ECMAScript's spec.

I'd recommend that you use an ordered structure, like an array, for the purpose of the problem:
var db = [
  {key: 'a', value: 1},
  {key: 'b', value: 2},
  {key: 'c', value: 3}
];
Then the next function can be something like:
var next = function(db, key) {
  for (var i = 0; i < db.length; i++) {
    if (db[i].key === key) {
      return db[i + 1] && db[i + 1].value;
    }
  }
};
In case key does not exist on db or it was the last one, next returns undefined. if you're never going to ask for the next of the last item, you can simplify that function by removing the ternary && operator and returning db[i + 1].value directly.

You can also use some of Underscore.js utility methods to make next simpler:
var next = function(db, key) {
  var i = _.pluck(db, 'key').indexOf(key);
  return i !== -1 && db[i + 1] && db[i + 1].value;
};
(in this case next could return false sometimes... but it's still a falsy value :))



Now, a more pragmatic answer could be that, as most browsers will respect the order in which an object was initialized when iterating it, you can just iterate it with a for in loop as the other answers suggest. I'd recommend using Object.keys to simplify the job of iterating over the array:
// Assuming that db is an object as defined in the question.
var next = function(db, key) {
  var keys = Object.keys(db)
    , i = keys.indexOf(key);
  return i !== -1 && keys[i + 1] && db[keys[i + 1]];
};


                        
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