如何在Javascript中通过键名和值获取json的子级部分？

Question

I got a json like:

var jsonData = {
    "id": 0,
    "content": "abc",
    "children" : [{
        "id": 1,
        "content": "efg",
        "children" : []
        }
        {
        "id": 2,
        "content": "hij",
        "children" : []
        }
    ]}

I just wanna get a children part of a json by searching correct key and value. Like

 if(id == 2)

then I can get jsonData.children[1] , and then I can do other things on this object I got. It's like a more efficient way which like indexOf()

It reminds me of using Hashtable in Java and C#. Well javascript seems like have no hashtable.

So, is there any way to solve this problem?

Answer 1

You can use filter :

var idToMatch = 2;
var matches = jsonData.children.filter(function (el) {
    return el.id === idToMatch;
});

UPDATE: Added recursive case

To expand this to the recursive case to at least provide an alternate approach to the much more elegant approach from the answer from @elclanrs above (which is the best answer here), but the below is added just for completeness.

var matches = [];
function findMatches(children, idToMatch) {
    if (children && Array.isArray(children)) {
        var newMatches = children.filter(function (el) {
            return (el.id === idToMatch);
        });
        Array.prototype.push.apply(matches, newMatches);
        for (var i = 0; i < children.length; i++)
            findMatches(children[i].children, idToMatch);
    }
}
findMatches(jsonData.children, 3);
console.log(matches);

JS Fiddle: http://jsfiddle.net/vafwg3kf/

Answer 2

You can use recursion and a reducer:

function find(pred, coll) {
  return coll.reduce(function(acc, obj) {
    if (pred(obj)) {
      return obj
    } else if (obj.children.length) {
      return find(pred, obj.children)
    } else {
      return acc
    }
  },null)
}

find(function(o){return o.id===2}, [jsonData])
//^ {id: 2, content: 'hij', children: []}

If no object with that id is found then it will return null .

Answer 3

Javascript objects are by default Maps. For instance,

var child = {}
child[1] = {"id": 1, "content": "efg"}
child[2] = { "id": 2,"content": "hij"}

you could retrieve the value like

var value = child[1].content;

Hope this helps!

Answer 4

This may be a way. It is inspired by @Jason W , @Mr.Green and @elclanrs .

I tried this, and it did work actually.

However, there is still some questions confused me about why it could work like this, and i will post my question later. Please check it out if you can help me.

var dataMap = {};

function matchData (jsonObj) {
  dataMap[jsonObj.id] = jsonObj;

  if (jsonObj.children.length > 0) {
    for (var i = 0; i < jsonObj.children.length; i++) {
      dataMap[jsonObj.children[i].id] = jsonObj.children[i];

      if (jsonObj.children[i].children > 0) {
        matchData(jsonObj.children[i]);
      }
    }
  }
}

matchData(jsonData);
console.log(dataMap[2]); 
//you will get "{"id": 2,"content": "hij","children" :[]}