Loop through object array with javascript

Question

I'm trying to loop through the following :

{
 "machine": [{
 "cost_center": "15023 DC1 M3 - Hassia1",
 "item": [{
 "batchno": "367721",
 "itemno": "12028"
 }, {
 "batchno": "367722",
 "itemno": "12328"
 }, {
 "batchno": "367723",
 "itemno": "12608"
 }]
 }, {
 "cost_center": "15033 DC1 M4 - Hamba",
 "item": [{
 "batchno": "367729",
 "itemno": "11850"
 }, {
 "batchno": "367730",
 "itemno": "11851"
 }, {
 "batchno": "367731",
 "itemno": "11852"
 }]
 }, {
 "cost_center": "15043 DC1 M5 - 1KG Machine",
 "item": {
 "batchno": "367732",
 "itemno": "12592"
 }
 }]
}

var json = '{"machine":[{"cost_center":"15023 DC1 M3 - Hassia1","item":[{"batchno":"367721","itemno":"12028"},{"batchno":"367722","itemno":"12328"},{"batchno":"367723","itemno":"12608"}]},{"cost_center":"15033 DC1 M4 - Hamba","item":[{"batchno":"367729","itemno":"11850"},{"batchno":"367730","itemno":"11851"},{"batchno":"367731","itemno":"11852"}]},{"cost_center":"15043 DC1 M5 - 1KG Machine","item":{"batchno":"367732","itemno":"12592"}}]}';
var obj = JSON.parse(json);
var db = obj.machine;
for (var m in db) {
 if (db.hasOwnProperty(m)) {
 var item = db[m].item;
 console.log('cost_center ' + m + ' = ' + db[m].cost_center);
 for (var i in item) {
 if (item.hasOwnProperty(i)) {
 var prod = item[i];
 console.log('-itemno ' + i + ' ' + prod.itemno);
 }
 }
 }
}

I have found similar question here but the difference lay on my data, my first 2 cost_centers have arrays as elements, my the 3rd one isn't an array.

cost_center 0 = 15023 DC1 M3 - Hassia1
-itemno 0 12028
-itemno 1 12328
-itemno 2 12608
cost_center 1 = 15033 DC1 M4 - Hamba
-itemno 0 11850
-itemno 1 11851
-itemno 2 11852
cost_center 2 = 15043 DC1 M5 - 1KG Machine
-itemno batchno undefined
-itemno itemno undefined

How can I loop through everything and still get all the values from the cost_center which doesn't contain an array ? Thanks

• Anurag Singh Bisht: You should probably mention the desired output so that people can help and see what you are doing wrong.
• Muhaimin: You repeat the object looping within it by perform some 'if'
• Jonathan: if you run the code, you can actually see what I'm talking about. but I will edit the question. thanks @AnuragSinghBisht
• Deepak Kamat: Beautify the JSON object maybe,
• a45b: Why the last item is not an array of objects?

Answer 1

No need for hasOwnProperty, and item.constructor === Array can be used to check:

var db = JSON.parse('{"machine":[{"cost_center":"15023 DC1 M3 - Hassia1","item":[{"batchno":"367721","itemno":"12028"},{"batchno":"367722","itemno":"12328"},{"batchno":"367723","itemno":"12608"}]},{"cost_center":"15033 DC1 M4 - Hamba","item":[{"batchno":"367729","itemno":"11850"},{"batchno":"367730","itemno":"11851"},{"batchno":"367731","itemno":"11852"}]},{"cost_center":"15043 DC1 M5 - 1KG Machine","item":{"batchno":"367732","itemno":"12592"}}]}').machine;
for (var m = 0; m < db.length; m++) 
{
 var e = db[m], item = e.item;
 console.log('cost_center ' + m + ' = ' + e.cost_center);
 if (item.constructor === Array)
 for (var i = 0; i < item.length; i++) 
 console.log(' itemno ' + i + ' = ' + item[i].itemno);
 else
 console.log(' itemno 0 = ' + item.itemno);
}

• Jonathan: what does the constructor do? and why does your if statement works without closure?
• Slai: @Jonathan it compares the variable constructor to the Array constructor. Suposedly it's the fastest way to check if a variable is Array.Curly braces are optional for one statement (not one line) stackoverflow.com/questions/7117873/…

Answer 2

Instead of using for-in to loop through the array, you can use forEach property.

Also, if your last element does not contains an array, I am assuming it will always be an object. So to test that, you can check for length of array. If length exists than it's an array and you can loop to get the answer. If not then it's an object, so you can directly print the values.

var json = '{"_vger_record_id":"2409247","ExtraData":"","machine":[{"_vger_record_id":"2409248","cost_center":"15023 DC1 M3 - Hassia1","ExtraData":"","item":[{"_vger_record_id":"2409249","batchno":"367721","itemno":"12028"},{"_vger_record_id":"2409250","batchno":"367722","itemno":"12328"},{"_vger_record_id":"2409251","batchno":"367723","itemno":"12608"}]},{"_vger_record_id":"2409257","cost_center":"15033 DC1 M4 - Hamba","ExtraData":"","item":[{"_vger_record_id":"2409258","batchno":"367729","itemno":"11850"},{"_vger_record_id":"2409259","batchno":"367730","itemno":"11851"},{"_vger_record_id":"2409260","batchno":"367731","itemno":"11852"}]},{"_vger_record_id":"2409261","cost_center":"15043 DC1 M5 - 1KG Machine","ExtraData":"","item":{"_vger_record_id":"2409262","batchno":"367732","itemno":"12592"}}]}';
var obj = JSON.parse(json);
var db = obj.machine;
db.forEach(function(m) {
 console.log('cost_center = ' + m.cost_center); 
 if(m.item.length) {
 m.item.forEach(function(i) {
 console.log('-itemno = ' + i.itemno);
 });
 } else {
 console.log('-itemno = ' + m.item.itemno);
 }
 
});

• Jonathan: Thanks, what advantage forEach has over For-in?
• charlietfl: Not a safe test by itself...could be an empty array with no length
• Anurag Singh Bisht: It's a utility of array through which you can easily iterate through arrays. for -in is not useful for this purpose
• Anurag Singh Bisht: I have stated that I am assuming that it will be object if it's not an array.
• charlietfl: Empty array is still an array