How do I iterate over a JSON structure?

I have the following JSON structure:

[{ "id":"10", "class": "child-of-9" }, { "id": "11", "classd": "child-of-10" }]

How do I iterate over it using JavaScript?

var arr = [ {"id":"10", "class": "child-of-9"}, {"id":"11", "class": "child-of-10"}];
    
for (var i = 0; i < arr.length; i++){
  document.write("<br><br>array index: " + i);
  var obj = arr[i];
  for (var key in obj){
    var value = obj[key];
    document.write("<br> - " + key + ": " + value);
  }
}

note: the for-in method is cool for simple objects. Not very smart to use with DOM object.

Taken from jQuery docs:

var arr = [ "one", "two", "three", "four", "five" ];
var obj = { one:1, two:2, three:3, four:4, five:5 };

jQuery.each(arr, function() {
  $("#" + this).text("My id is " + this + ".");
  return (this != "four"); // will stop running to skip "five"
});

jQuery.each(obj, function(i, val) {
  $("#" + i).append(document.createTextNode(" - " + val));
});

Use for...of:

var mycars = [{name:'Susita'}, {name:'BMW'}];

for (var car of mycars) 
{
  document.write(car.name + "<br />");
}

Result:

Susita
BMW

Please let me know if it is not easy:

var jsonObject = {
  name: 'Amit Kumar',
  Age: '27'
};

for (var prop in jsonObject) {
  alert("Key:" + prop);
  alert("Value:" + jsonObject[prop]);
}

If this is your dataArray:

var dataArray = [{"id":28,"class":"Sweden"}, {"id":56,"class":"USA"}, {"id":89,"class":"England"}];

then:

$(jQuery.parseJSON(JSON.stringify(dataArray))).each(function() {  
         var ID = this.id;
         var CLASS = this.class;
});

Copied and pasted from http://www.w3schools.com, there is no need for the JQuery overhead.

var person = {fname:"John", lname:"Doe", age:25};

var text = "";
var x;
for (x in person) {
    text += person[x];
}

RESULT: John Doe 25

mootools example:

var ret = JSON.decode(jsonstr);

ret.each(function(item){
    alert(item.id+'_'+item.classd);
});

You can use a mini library like objx - http://objx.googlecode.com/

You can write code like this:

var data =  [ {"id":"10", "class": "child-of-9"},              {"id":"11", "class": "child-of-10"}];

// alert all IDs
objx(data).each(function(item) { alert(item.id) });

// get all IDs into a new array
var ids = objx(data).collect("id").obj();

// group by class
var grouped = objx(data).group(function(item){ return item.class; }).obj()

There are more 'plugins' available to let you handle data like this, see http://code.google.com/p/objx-plugins/wiki/PluginLibrary

With nested objects, it can be retrieve as by recursive function:

function inside(events)
  {
    for (i in events) {
      if (typeof events[i] === 'object')
        inside(events[i]);
      else
      alert(events[i]);
    }
  }
  inside(events);

where as events is json object.

Marquis Wang's may well be the best answer when using jQuery.

Here is something quite similar in pure JavaScript, using JavaScript's forEach method. forEach takes a function as an argument. That function will then be called for each item in the array, with said item as the argument.

Short and easy:

var results = [ {"id":"10", "class": "child-of-9"}, {"id":"11", "classd": "child-of-10"} ];

results.forEach(function(item) {
    console.log(item);
});

this is a pure commented JavaScript example.

  <script language="JavaScript" type="text/javascript">
  function iterate_json(){
			// Create our XMLHttpRequest object
			var hr = new XMLHttpRequest();
			// Create some variables we need to send to our PHP file
			hr.open("GET", "json-note.php", true);//this is your php file containing json
			
			hr.setRequestHeader("Content-type", "application/json", true);
			// Access the onreadystatechange event for the XMLHttpRequest object
			hr.onreadystatechange = function() {
				if(hr.readyState == 4 && hr.status == 200) {
					var data = JSON.parse(hr.responseText);
					var results = document.getElementById("myDiv");//myDiv is the div id
					for (var obj in data){
					results.innerHTML += data[obj].id+ "is"+data[obj].class + "<br/>";
					}
				}
			}

			hr.send(null); 
		}
</script>
<script language="JavaScript" type="text/javascript">iterate_json();</script>// call function here

var jsonString = `{
    "schema": {
        "title": "User Feedback",
        "description": "so",
        "type": "object",
        "properties": {
            "name": {
                "type": "string"
            }
        }
    },
    "options": {
        "form": {
            "attributes": {},
            "buttons": {
                "submit": {
                    "title": "It",
                    "click": "function(){alert('hello');}"
                }
            }
        }
    }
}`;

var jsonData = JSON.parse(jsonString);

function Iterate(data)
{
    jQuery.each(data, function (index, value) {
        if (typeof value == 'object') {
            alert("Object " + index);
            Iterate(value);
        }
        else {
            alert(index + "   :   " + value);
        }
    });
}

Iterate(jsonData);

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

Another solution to navigate through the JSON document is JSONiq (implemented in the Zorba engine), where you can write something like this:

let $doc := [
  {"id":"10", "class": "child-of-9"},
  {"id":"11", "class": "child-of-10"}
]
for $entry in members($doc) (: binds $entry to each object in turn :)
return $entry.class         (: gets the value associated with "class" :)

You can run it on http://public.rumbledb.org:9090/public.html