Develop Reference

Better / Faster way to modify all matched property found under different depth from a nesting object

I receive a json from an API that I need to parse and modify one property value. Thing is, the nesting structure of the json data I receive are inconsistent and I have no control over it.
This will prohibit me to specify to look under a certain depth like parsedJson.children[0].property since the property I'm looking for could be found on a different nesting level like parsedJson.children[0].children[0].property on the next iteration.
I currently do it like this, and it works
var parsedJson = JSON.parse('{"a":[{"a1":[{"p":0},{"np":1}]}],"b":[{"p":0},{"np":1}],"c":[{"c1":[{"c2":[{"p":0}]},{"np":1}]}]}')
console.log("before modify")
console.log(parsedJson)
modifyProperty(parsedJson,"p",1);
function modifyProperty(obj,prop,val){
for (var key in obj){
if (key == prop){
obj[key] = val;
}
modifyProperty(obj[key],prop,val);
}
}
console.log("after modify")
console.log(parsedJson)
but I'm afraid later on, if I received a json from API that contains a lot more data and far deeper nesting levels that it may affect performance since this would need to recursively check all children nodes one by one.
Is there a better / faster way to this?

You can pass a second parameter to JSON.parse that recursively transforms all desired property values:
var parsedJson = JSON.parse(
'{"a":[{"a1":[{"p":0},{"np":1}]}],"b":[{"p":0},{"np":1}],"c":[{"c1":[{"c2":[{"p":0}]},{"np":1}]}]}',
(key, val) => key === 'p' ? 1 : val
);
console.log(parsedJson);

Node.JS behaves strange

I have a variable called uids
var uids = [];
Then I write some value to it property
uids[16778923] = "3fd6335d-b0e4-4d77-b304-d30c651ed509"
But before it
if (!uids[user.id]) {
uids[user.id] = generateKey(user);
}
This thing behaves ok. If I try to get the value of it property
uids[currentUser.id]
It will give me a value of this property. If I try to call some methods like
Object.keys(uids);
It will give me, what I expected. And here the mystery comes...
uids;
RAM rest in piece. See the node eating ram
I am very confused now. What's wrong?

This is because you are creating a huge array and node will reserve memory for it - who knows what comes. I'd say that's a scenario where you would use a Map (or a plain object, but Map feels better here.
var uids = new Map();
var key = 456464564564654;
if (! uids.has(key)) {
uids.set(key, generateKey(user))
}

You are creating an empty array (length is zero), then you assign some value to an arbitrary index. This will make the array grow as big as the index and assign the value to that index. Look at this example using node.js REPL:
> var a = []
undefined
> a[5] = "something"
'something'
> a
[ , , , , , 'something' ]
> a.length
6
Instead of creating an array, you could create a Map() or an common javascript object (singleton). Javascript objects behave like Maps but only Strings can be used as keys. If you assign a Number to be key, javascript will convert it to String automatically.
Personally, I would go with objects because they perform better. Instantiating an object takes longer than instantiating a Map (and it doesn't seem like you need to create several groups of "uids"), but once done, adding new keys and retrieving values from any key in faster when using common objects. At least that's how things go in my node.js v6.7.0 on ubuntu 14.04 but you could try for yourself. And it would also make the least alteration to your code.
var uids = {} // common/ordinary empty javascript object instead of array.
if (!uids[user.id]) { // getting value from one key works the same.
uids[user.id] = generateKey(user) // assignment works the same.
}
////
uids[16778923] = "3fd6335d-b0e4-4d77-b304-d30c651ed509" // key will be "16778923".
uids[16778923] // getting value for key "16778923" can be done using 16778923 instead of "16778923".
////
uids[currentUser.id] // still returning values like this.
Object.keys(uids) // still returning an array of keys like this. but they are all Strings.

How do I sort a JSON object by a nested value?

I have an ajax call that returns a JSON object that is pretty complex and I'm having a hard time sorting it.
My call:
$.post('/reports-ajax',arguments, function(data) {}
The response:
{
"10001":{
"unitname":"Fort Worth",
"discounts":{"12-02-2012":"34.810000","12-03-2012":"20.810000","12-04-2012":"27.040000"},
"gross":{"12-02-2012":"56.730000","12-03-2012":"19.350000","12-04-2012":"66.390000"},
"net":{"12-02-2012":"61.920000","12-03-2012":"98.540000","12-04-2012":"39.350000"},
"discounts_total":82.66,
"gross_total":82.47,
"net_total":99.81,
"number":10001
},
"10002":{
"unitname":"Dallast",
"discounts":{"12-02-2012":"12.600000","12-03-2012":"25.780000","12-04-2012":"47.780000","12-05-2012":"45.210000"},
"gross":{"12-02-2012":"29.370000","12-03-2012":"91.110000","12-04-2012":"60.890000","12-05-2012":"51.870000"},
"net":{"12-02-2012":"16.770000","12-03-2012":"65.330000","12-04-2012":"13.110000","12-05-2012":"06.660000"},
"discounts_total":131.37,
"gross_total":33.24,
"net_total":101.87,
"number":10002
},
"32402":{
"unitname":"Austin",
"discounts":{"12-05-2012":"52.890000","12-02-2012":"22.430000","12-03-2012":"58.420000","12-04-2012":"53.130000"},
"gross":{"12-05-2012":"25.020000","12-02-2012":"2836.010000","12-03-2012":"54.740000","12-04-2012":"45.330000"},
"net":{"12-04-2012":"92.200000","12-05-2012":"72.130000","12-02-2012":"13.580000","12-03-2012":"96.320000"},
"discounts_total":186.87,
"gross_total":161.1,
"net_total":174.23,
"number":32402
}
}
I go over the function with a standard each call and do some awesome stuff with highcharts but now I'm trying to sort the responses by the net_total call and I can't figure it out.
I tried .sort() and it errors out that its not a function. I've been reading for a while but guess I'm not finding the right results. This looked promising: Sorting an array of JavaScript objects but it failed with the .sort is not a function. It seems most .sort are on [] arrays not full objects..
Any help would be greatly appreciated.

Sorting objects doesn't make sense since object keys have no positional value. For example, this:
{ a:1, b:2 }
and this:
{ b:2, a:1 }
are exactly the same object. They're not just similar, they're the same.
Nothing in javascript per se gives object keys any positional value. Some people perhaps are mistaken in the belief that:
for (var key in obj) {
iterates through the object keys in a specific sequence. But this is wrong. You should always assume that the for .. in loop processes object keys in random order, always, all the time.
Obviously, if you're going to write a web browser, you're not going to implement a random number generator to parse a for .. in loop. Therefore most web browsers have an accidental stability to how the for .. in loop processes object keys.
Developers who learn javascript by playing around with the browser may figure out that their browser iterates through objects in alphabetical order for example, or the order the keys were added to the object. But this is totally accidental and cannot be relied upon. The browser vendor may change this behavior in the future without violating any backwards compatability (except with buggy scripts written by people who believe objects have a sort order). Not to mention that different browsers have different implementations of javascript and therefore not necessarily have the same internal key ordering of objects.
All the above is besides the point. "Key sort order" does not make any sense in javascript and any behavior observed is merely implementation detail. In short, javascript object does not have key order, just assume it's random.
Solution
Now, what you're really trying to do is not sort the object (you can't, it doesn't make sense). What you're really trying to do is process the object attributes in a specific order. The solution is to simply create an array (which has sorting order) of object keys and then process the object using that array:
// First create the array of keys/net_total so that we can sort it:
var sort_array = [];
for (var key in Response) {
sort_array.push({key:key,net_total:Response[key].net_total});
}
// Now sort it:
sort_array.sort(function(x,y){return x.net_total - y.net_total});
// Now process that object with it:
for (var i=0;i<sort_array.length;i++) {
var item = Response[sort_array[i].key];
// now do stuff with each item
}

What you have there isn't an array and has no order, so you'll have to transform it into an array so you can give it order.
Vaguely:
var array = [];
$.each(data, function(key, value) {
array.push(value);
});
array.sort(function(a, b) {
return a.net_total - b.net_total;
});
Live Example | Source
As GolezTroi points out in the comments, normally the above would lose the key that each entry is stored under in data and so you'd add it back in the first $.each loop above, but in this case the entries already have the key on them (as number), so there's no need.
Or you can replace the first $.each with $.map:
var array = $.map(data, function(entry) {
return entry;
});
// ...and then sort etc.
...whichever you prefer.

getting the amount of properties in an object then getting the last one of them in a for loop

This should be very easy but I don't know how to do it.
I have this object:
var obj = eval(result);
Now I want to know how many properties contains to put it in a loop
var finalAmount = obj.length;
Now I go for the loop
for (var i in obj) {
--- some other code in here
Now here the problem I need to do something when the loop reaches the final property of the obj, so this is what Ive tried:
if (i+1 == finalamount){
//do something
} else {
//do something else
}
so basically using the i as a pointer to compare it to the var that contains how many items there are and when finding the final one of the loop then do something...

In this case i is not necessarily numeric, and so i+1 may not give you the desired results. You should set up a separate counter variable that you increment at the end of each loop iteration.

In your case obj must be an Array. If it is not, i+1 throws error.
The for-in loop does not ensure any sequence order, even it is an Array, it is only used to iterate unordered properties. You need traditional for(index=0;index<length;index++) (if it is an Array)
If your obj variable is an Object instead of Array, you can't get "last property" only with object data structure, it must provide more information (property order).

Question about the for loop in javascript?

In the following code why the variable 'a' refer to the index rather than the value ?
for (var a in Values) {
alert(Values[a]);
}

That's by design. It's trivial to get a value in an array when you know its key, but it's much harder to get a key given a value. Values can be duplicated, so how do you know which key should be used? But a key's unique, so given a key, there's only ever one value to retrieve. So, the for loop will iterate over the keys, and it's trivial to get the associated value.

Think of a JavaScript Array as a normal Object with a special property named length (actually, it a bit more complex). So the for..in loop behaviour is identical as for other objects:
var a = new Array();
a[1] = "a";
alert(a.length); // 2
alert(a[0]); // undefined
a[1000] = "b"
alert(a.length); // 1001
a[-1] = "c";
alert(a[-1]); // c
a.abc="why not";
for(var key in a)
{
alert(key+"="+a[key]);
}
// 1=a
// 1000=b
// -1=c
// abc=why not
Also note that you can have gaps within your array without having to pay the memory price.

There is a for each...in loop that does exactly that - enumerates only values. Coming soon to a browser near you.
for each(var a in Values) {
..
}
For arrays, there is a new function forEach which achieves the same.
someArray.forEach(function(value) {
..
});