Retrieving a property of a JSON object by index?_问答_开发者

Assuming this JSON object:

var obj = {
    "set1": [1, 2, 3],
    "set2": [4, 5, 6, 7, 8],
    "set3": [9, 10, 11, 12]
};

The "set2" property may be retrieved like so:

obj["set2"]

Is there a way to retrieve the "set2" property by index? It is the second property of the JSON object. This does not work (of course):

obj[1]

So, let's say that开发者_StackOverflow I want to retrieve the second property of the JSON object, but I don't know its name - how would I do it then?

Update: Yes, I understand that objects are collections of unordered properties. But I don't think that the browsers mess with the "original" order defined by the JSON literal / string.

Objects in JavaScript are collections of unordered properties. Objects are hashtables.

If you want your properties to be in alphabetical order, one possible solution would be to create an index for your properties in a separate array. Just a few hours ago, I answered a question on Stack Overflow which you may want to check out:

Iterating over a JavaScript object in sort order based on particular key value of a child object

Here's a quick adaptation for your object¹:

var obj = {
    "set1": [1, 2, 3],
    "set2": [4, 5, 6, 7, 8],
    "set3": [9, 10, 11, 12]
};

var index = [];

// build the index
for (var x in obj) {
   index.push(x);
}

// sort the index
index.sort(function (a, b) {    
   return a == b ? 0 : (a > b ? 1 : -1); 
});

Then you would be able to do the following:

console.log(obj[index[1]]);

The answer I cited earlier proposes a reusable solution to iterate over such an object. That is unless you can change your JSON to as @Jacob Relkin suggested in the other answer, which could be easier.

¹ You may want to use the hasOwnProperty() method to ensure that the properties belong to your object and are not inherited from Object.prototype.

I know this is an old question but I found a way to get the fields by index. You can do it by using the Object.keys method.

When you call the Object.keys method it returns the keys in the order they were assigned (See the example below). I tested the method below in the following browsers:

Google Chrome version 43.0
Firefox version 33.1
Internet Explorer version 11

I also wrote a small extension to the object class so you can call the nth key of the object using getByIndex.

// Function to get the nth key from the object
Object.prototype.getByIndex = function(index) {
  return this[Object.keys(this)[index]];
};

var obj1 = {
  "set1": [1, 2, 3],
  "set2": [4, 5, 6, 7, 8],
  "set3": [9, 10, 11, 12]
};

var obj2 = {
  "set2": [4, 5, 6, 7, 8],
  "set1": [1, 2, 3],
  "set3": [9, 10, 11, 12]
};

log('-- Obj1 --');
log(obj1);
log(Object.keys(obj1));
log(obj1.getByIndex(0));


log('-- Obj2 --');
log(obj2);
log(Object.keys(obj2));
log(obj2.getByIndex(0));


// Log function to make the snippet possible
function log(x) {
  var d = document.createElement("div");
  if (typeof x === "object") {
    x = JSON.stringify(x, null, 4);
  }
  d.textContent= x;
  document.body.appendChild(d);
}

No, there is no way to access the element by index in JavaScript objects.

One solution to this if you have access to the source of this JSON, would be to change each element to a JSON object and stick the key inside of that object like this:

var obj = [
    {"key":"set1", "data":[1, 2, 3]},
    {"key":"set2", "data":[4, 5, 6, 7, 8]},
    {"key":"set3", "data":[9, 10, 11, 12]}
];

You would then be able to access the elements numerically:

for(var i = 0; i < obj.length; i++) {
    var k = obj[i]['key'];
    var data = obj[i]['data'];
    //do something with k or data...
}

Simple solution, just one line..

var obj = {
    "set1": [1, 2, 3],
    "set2": [4, 5, 6, 7, 8],
    "set3": [9, 10, 11, 12]
};

obj = Object.values(obj);

obj[1]....

Here you can access "set2" property following:

    var obj = {
        "set1": [1, 2, 3],
        "set2": [4, 5, 6, 7, 8],
        "set3": [9, 10, 11, 12]
    };

    var output = Object.keys(obj)[1];

Object.keys return all the keys of provided object as Array..

Jeroen Vervaeke's answer is modular and the works fine, but it can cause problems if it is using with jQuery or other libraries that count on "object-as-hashtables" feature of Javascript.

I modified it a little to make usable with these libs.

function getByIndex(obj, index) {
  return obj[Object.keys(obj)[index]];
}

You could iterate over the object and assign properties to indexes, like this:

var lookup = [];
var i = 0;

for (var name in obj) {
    if (obj.hasOwnProperty(name)) {
        lookup[i] = obj[name];
        i++;
    }
}

lookup[2] ...

However, as the others have said, the keys are in principle unordered. If you have code which depends on the corder, consider it a hack. Make sure you have unit tests so that you will know when it breaks.

"""
This could be done in python as follows.
Form the command as a string and then execute
"""
context = {
    "whoami": "abc",
    "status": "0",
    "curStep": 2,
    "parentStepStatus": {
        "step1":[{"stepStatus": 0, "stepLog": "f1.log"}],
        "step2":[{"stepStatus": 0, "stepLog": "f2.log"}]
    }
}
def punc():
          i = 1
          while (i < 10):
              x = "print(" + "context" + "['parentStepStatus']" + "['%s']"%("step%s")%(i) + ")"
              exec(x)
              i+=1
punc()

There is no "second property" -- when you say var obj = { ... }, the properties inside the braces are unordered. Even a 'for' loop walking through them might return them in different orders on different JavaScript implementations.

it is quite simple...

var obj = {
    "set1": [1, 2, 3],
    "set2": [4, 5, 6, 7, 8],
    "set3": [9, 10, 11, 12]
};

jQuery.each(obj, function(i, val) {
	console.log(i); // "set1"
	console.log(val); // [1, 2, 3]
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

var obj = {
    "set1": [
        1,
        2,
        3
    ],
    "set2": [
        4,
        5,
        6,
        7,
        8
    ],
    "set3": [
        9,
        10,
        11,
        12
    ]
};

var outputKeys = Object.keys(obj)[1];

var outputValues = Object.values(obj)[1];
//outputKeys would be "set2"`enter code here`
//outPutValues would be [4,5,6,7,8]

My solution:

Object.prototype.__index=function(index)
                         {var i=-1;
                          for (var key in this)
                              {if (this.hasOwnProperty(key) && typeof(this[key])!=='function')
                                  {++i;
                                  }
                               if (i>=index)
                                  {return this[key];
                                  }
                              }
                          return null;
                         }
aObj={'jack':3, 'peter':4, '5':'col', 'kk':function(){alert('hell');}, 'till':'ding'};
alert(aObj.__index(4));