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Checking for the last element in a JQuery each function

I have an object that I am iterating through using JQuery's each function. However, the solution posted in this stack overflow post doesn't work when I tried using the length property. I got undefined in the console when I tried getting a length property value, which I believe this is because I am iterating through an object and not an array.
My code:
$.each(attributes, function(key, value) {
attrKey = key;
attrVal = value;
console.log(attributes.length); //returns undefined
//do something if it is the last element
});

Try plain Javascript instead:
for (var key in attributes) {
var value = attributes[key];
// process key,value...
}
Edit:
If you're trying to get the last key/value in an object, you can't. Javascript objects are unordered, meaning that they do not keep track of when additional key/value assignments are made. If order is important, I would recommend changing attributes be an array of objects, where each object is a single key/value, or use a 3rd party library, like this - https://github.com/trentrichardson/Ordering.
If you'd like to get the number of keys in attributes, use Object.keys:
Object.keys(attributes).length

Try
var index = 1;
$.each(attributes, function(key, value) {
if(Object.keys(attributes).length == index)
{
// Do something
}
index++;
});

per #PaulFrench's comment:
length = Object.keys(attributes).length;
if(n < length) {
//do something
}

accessing an object from function arguments [duplicate]

This question already has answers here:
Accessing nested JavaScript objects and arrays by string path
(44 answers)
Closed 7 years ago.
I tried to make it by myself, but I don't know if this is possible
function smth(){
var temp = [];
for(var i = arguments.length -1; i > 2; i-=1){
var temp2 = [];
temp.push(arguments[i]);
temp2.push(temp);
temp = temp2;
console.log(temp);
}
// I need to get array in this form
var something = item['collections']['0']['name'];
}
smth('collection','0','name');
edit:
Okay, maybe I haven't given you enough information.
I've got a JSON object, and I'm making a filter function, and I'd like to make it more reusable because now I have hard-coded item.collections[0].name,
and sometimes I need use item.parameters.name, and I will use it few a more times
$scope.$watch(name, function (newValue, oldValue) {
if (newValue !== oldValue) {
$scope.productsChucks = myFilter(array, function(item) {
//console.log(item['collections']['0']['name']);
if (item.collections[0].name == $scope[compareWith]) {
return item;
}
});
}
});

I think you stated your question completely wrong, IMHO it's a typical XY problem https://meta.stackexchange.com/a/66378
Anyway, based on your edit, what I think you really want is to get some nested properties of an object using a string in form "item.parameters.name".
The simplest way to do this is to use some kind of a helper library, eg. lodash:
_.get(item, 'parameters.name') // returns item.parameters.name
_.get(item, 'collections[0].name') // returns item.collections[0].name
Using that your code will look similar to this:
// path is a string given as the parameter to the filter
if (_.get(item, path) === $scope[compareWith]) {
return item;
}
Your function smth will now take only one argument:
smth('collection[0].name');
More information about lodash can be found here https://lodash.com/docs#get
If you think you don't need whole lodash you can implement this single function by yourself, take a look here https://stackoverflow.com/a/6491621/704894

If you need to access it this way:
var something = item['collections']['0']['name'];
Then it's not an array, but actually an object accessed with index notation. You can do it this way:
function smth() {
var temp = {};
var root = temp;
for (var i = 0; i < arguments.length; i++) {
temp[arguments[i]] = {};
temp = temp[arguments[i]];
}
return root;
}
console.log(JSON.stringify(smth('collection', '0', 'name'), null, 2));

Assigning a javascript object with and object inside an array

I am just curious about this.
Let's say I have an array of objects and I create 1 object, lets name the array of objects items and the object item.
I want to get a particular item in my array of items by using the following code:
//gets an item base on ID
function get_item(td){
var item = undefined;
$.each(items, function(i, val) {
if(val.item_id == td){
item = val;
}
});
return item;
}
The get_item() basically gets an object matched with the supplied id.
So my question is this. What if I changed the properties of item will it also changed the properties of an object associated with it within the array?
Thank you very much!

What if I changed the properties of item will it also changed the properties of an object associated with it within the array?
Yes.
Objects are not copied. Instead, references to the objects are passed around. Simplest example:
var a = [];
var b = a;
b.push(1);
console.log(a); // logs [1]
Many object-oriented programming languages work like this.

The value of the object inside the array will also change because it's a reference. If you want more information I highly recommend reading Objects and Prototypes.
If you don't want it to change then you should use something like lodash's _.clone() function.
Also you could use filter to get the object:
function get_item(td){
return items.filter(function(item) {
return item.id === td;
})[0];
}

You can update you function to:
var data= array();
function get_item(propertyValue, propertyName){
var retval;
for(var i = 0; i < data.length; i++){
if(data[i][propertyName]==propertyValue){
retval = data[i];
break;
}
}
return retval;
}
Use it
var item1 = get_item(1,"id");
var item2 = get_item("john","name");

Javascript sort multi-dimensional array - a complete example?

I'm no Javascript expert and I'm having problems trying to glue together the various nuggets I find here and elsewhere regarding multi-dimensional arrays and sorting and wondered if someone could help me with a complete example?
I have managed to get to the point that I can populate a localStorage with data read in via Ajax.
The format of the rows is ...
(msgXXX) (Key1:Value1|Key2:Value2|Key3:Value3|...etc)
where
(msgXXX) is the localStorage key; and
(Key1:Value1|Key2:Value2|Key3:Value3|...etc) is the single concatenated localStorage data string
What I want to be able to do is convert all this to a multi-dimensional array to which I can apply various sorts. For example, one of the Keys is called "Timestamp" and the value is an integer representing seconds since the Unix epoch. I would like to sort all rows based on this Timestamp value (in descending order - ie latest first). Right now the dataset is just over 600 rows.
I'm comfortable I can do the extraction and slicing and dicing to get the data out of the localStorage, but I'm not even sure what I'm aiming for with regards to populating an array and then setting up the sort.
Can someone point me in the right direction?

You can go with something like this:
function create(line) {
var tokens = line.split("|");
var obj = {};
for (var i = 0; i < tokens.length; i++) {
tokens[i] = tokens[i].split(":");
obj[tokens[i][0]] = tokens[i][1];
}
return obj;
}
var arr = [];
for (....) { // iterate over the input that each line is of key/value format
arr.push(create(line));
}
function timestampSort(a, b) {
if (a == b)
return 0;
return a.timestamp < b.timestamp ? -1 : 1;
}
// to sort by timestamp
arr.sort(timestampSort);
This code creates an object per key/value line, in the format you gave. The object will have the keys as attributes. All of those objects are being pushed into an array, which is then being sorted by passing a compare function to the native sort method of array.
You can of course make as many compare functions as you want, each comparing by a different attribute/criteria.
You can read more about the sort method here: http://www.w3schools.com/jsref/jsref_sort.asp
EDIT
The sort method both changes the array itself and returns the array, so doing something like:
console.log(arr.sort(timestampSort));
Will both change the actual array and return it, and so the console.log will print it.
If you don't want to change the original array and have a copy of it that will get sorted you can:
var arr2 = arr.slice();
arr2.sort(timestampSort);
As for the keys in the array, what I wrote was intended to work only with this part of the line: Key1:Value1|Key2:Value2|Key3:Value3|...etc
So, to add support for the entire format, here's the modification:
function create(line) {
var parts = line.match(/^\(msg(\d+)\) \((.+)\)$/);
var tokens = parts[2].split("|");
var obj = { msgID: parts[1] };
for (var i = 0; i < tokens.length; i++) {
tokens[i] = tokens[i].split(":");
obj[tokens[i][0]] = tokens[i][1];
}
return obj;
}
If you apply this to the example you gave you'll get this:
arr is: [{
msgID: XXX,
Key1: Value1,
Key2: Value2,
Key3: Value3
}]
Hope this clears things for you.

sum index in JavaScript foreach

In the following code sample i get a strange behavior
var data = ['xxx', 'yyy'];
for (var i in data)
{
var a = i;
var b = data[i];
}
The two first iterations works just fine. I get index "0" and "1" in i, but then it loops one extra time and now the i is "sum". Is this by design or what is this extra iteration used for? The result in my case is always empty and it messes up my code. Is there a way to not do his extra loop?
BR
Andreas

It looks like you (or some other code you've included) have added extra properties onto the Array prototype. What you should be doing is checking to see whether the object you're iterating over actually has that property on itself, not on its prototype:
for (i in data) {
if (data.hasOwnProperty(i)) {
a = i;
b = data[i];
}
}
That said, you should never use for .. in on arrays. Use a regular for loop.
See here for more information: http://yuiblog.com/blog/2006/09/26/for-in-intrigue/

You are looping through an Array, not through an Object. For arrays it's better to use:
for (var i=0; i<data.length; i=i+1){
/* ... */
}
In your loop every property of the Array object is taken into account. That makes the for ... in loop for array less predictable. In your case it looks like sum is a property (method) that's added to Array.prototype elsewhere in your code.
There are more ways to loop through arrays. See for example this SO-question, or this one
Just for fun, a more esoteric way to loop an array:
Array.prototype.loop = function(fn){
var t = this;
return (function loop(fn,i){
return i ? loop(fn,i-1).concat(fn(t[i-1])) : [];
}(fn,t.length));
}
//e.g.
//add 1 to every value
var a = [1,2,3,4,5].loop(function(val){return val+1;});
alert(a); //=> [2,3,4,5,6]
//show every value in console
var b = [1,2,3,4,5].loop(function(val){return console.log(val), val;});

Here's a way to safely iterate.
var data = ['xxx', 'yyy'];
for (var i = 0; i < data.length; i++)
{
var a = i;
var b = data[i];
}
What you are getting is an method coming from extending the Array object, I guess you are using some library where is something like
Array.prototype.sum = function () {...};

Perhaps setting data like this would work better: var data = {0:'xxx', 1:'yyy'};

First of all data is an object. Try to add console.log(a); and console.log(b); inside your loop and you'll see.