Underscore pluck not working on array of models? - javascript

var currentVideos = this.get('items').pluck('video');
// TODO: Why does pluck not work here?
var currentVideosDurations = _.map(currentVideos, function (currentVideo) {
return currentVideo.get('duration');
});
var test = _.pluck(currentVideos, 'duration');
console.log("Test:", test);
I was wondering why my second pluck doesn't work, but my map works fine? I thought these were equivilant usages.
Here's a screenshot of a console log showing this.get('items') and the array of currentVideos.

The backbone model object doesn't store the properties you get from the model at the top level javascript object. The currentVideo backbone model object actually stores the attributes deeper within the javascript object, in (currentVideo.attributes).
_.pluck(currentVideos, 'duration') checks for the top level attribute (e.g. currentVideo['duration']), which doesn't exist.
The distinction is that Backbone Model objects are more sophisticated than basic javascript objects and don't get attributes by just retrieving object['attrName'].

I thought these were equivilant usages.
Nope. pluck is accessing properties with that name, but get is a method invocation. However, to shorten the map you can use invoke:
var currentVideosDurations = _.invoke(currentVideos, "get", "duration");

Related

Meteor Session variable not storing array

I'm working on a project with search option filters and they're updated via sessions, but I'm having some issues with the session variable actually taking the array. It works fine for non-array based values, but for instance when I pass an array with RegExp objects to be used in a mongo $in selector it doesn't work as expected. The functions work fine right up until it hits Session.set() in the code snippet below so I know I have to be doing something wrong with that:
Option.prototype.update = function () {
//updates session variable if static option
if (!this.isDynamic) {
if(Object.prototype.toString.call(this.value) === '[object Array]') {
var temp = this.value.slice(0);
Session.set(this.optionName, temp);
console.log(Session.get(this.optionName));
}
else {
Session.set(this.optionName, this.value);
}
};
};
for whatever reason instead of displaying the array with values in it, it displays
[Object], and the object in that array is empty. I've read the other Overflow posts on Session variables and arrays, and simply cloning the array before passing it doesn't seem to be working. Any idea what I'm doing wrong?
Your code is correct (although slightly convoluted). The problem is that Session only takes EJSON–able values, and regexes are not EJSON–able. From the perspective of EJSON, regex looks just like an empty object, and that's exactly what you get in the stored array. Similar problem would appear if you try to store object with custom prototype, or with private (not enumerable) properties: everything that is not serialized to EJSON is lost.
The solution here is to create your own serialization method that will work with regexes. For example, if you will always have a flat array of regexes, you could simply stringify them before storing:
var temp = _.map(this.value, function(regex) {
return regex.toString();
});

Cloning and manipulating nested object using forEach, map, or filter without modifying original object

I'm trying to get a handle on using .map, .filter to clone and modify a big nested JSON object based on a deeply nested property. With the below code, the original data and the filtered data both end up getting modified, but I'm trying to leave the original data intact. What I'm hoping to do is have the deeply nested concerns array emptied in the final filtered object for a given id, leaving the original data as the original complete data set.
var data {...};
var dataFilter = function dataBuild(data) {
var newData = data;
newData.service_requests = newData.service_requests.map((request) => {
request.concerns = request.concerns.filter((concern) => {
return concern.building_id == 2
});
return request;
});
return newData;
};
var filtered = dataFilter(data);
Here's a fiddle with what I'm trying to do with the full object in there.
http://jsbin.com/doyoqinoxo/edit?js,console
When you do:
var newData = data;
you are simply making a second reference to the same object, so:
newData.service_requests = ...
overwrites the value in data.service_requests.
It seems you want newData to be a copy of data, not a reference to the same object. There are plenty of posts here on how to copy a nested object (a so–called deep copy), e.g. What is the most efficient way to clone an object?, but please ignore the accepted answer unless you are using jQuery. Use one of the other answers, like this one.
JSIterator .map() creates the new array with the same number of elements or does not change the original array. There might be the problem with referencing if there is object inside the array as it copies the same reference, so, when you are making any changes on the property of the object it will change the original value of the element which holds the same reference.
The solution would be to copy the object, well, array.Splice() and [...array](spread Operator) would not help in this case, you can use JavaScript Utility library like Loadash or just use below mention code:
const newList = JSON.parse(JSON.stringify(orinalArr))

How to work with javascript object methods in Angularfire

I have an object that represents a restaurant order:
function order () {
this.customer_name = ''
this.menu = // menu object
}
extended with some object methods for business logic, like:
order.prototype.value = function() {
var total = 0;
for (var i = 0; i < this.menu.length; i++) {
// calculate the order value
}
return total;
}
In the angular controller orders get pushed onto an array when submitted (via ng-click from a button in the view):
var ref = new Firebase('https://myfirebase.firebaseio.com');
$scope.orders = [];
angularFire(ref, $scope, 'orders');
$scope.currentOrder = orderService;
$scope.submitOrder = function() {
$scope.orders.push($scope.currentOrder);
};
Once orders are pushed into the array, properties like orders[0].customer_name work, but methods like orders[0].value() don't.
It seems reasonable that Firebase/Angularfire would only be syncing JSON, but is there an approach that would allow me to keep order-related logic included with the order object, i.e without having to write $scope.getOrderValue(orders[0])?
There isn't a great way to do exactly what you want, since according to the Firebase FAQ:
At a low-level, we support basically the same data types as JSON: Strings, Numbers, Booleans, and Objects (which in turn contain Strings, Numbers, Booleans, and more Objects).
Which means you can store data but not functions. It seems like a clean way to accomplish the same thing would be to store the latest order value as a property of your order object, and have a method as part of your orderService that updates it whenever menu items are added or removed. Alternatively, do what you suggested and have a getOrderValue somewhere, but it probably still makes sense to put that in a service.
I actually had the same issue.
I wanted to add a method to my firebase object.
After looking in the latest angularfire docs I found that $extend can do just that
I didn't test it yet, but I think this is the way to go about it.

Javascript pushing objects into array changes entire array

I'm using a specific game making framework but I think the question applies to javascript
I was trying to make a narration script so the player can see "The orc hits you." at the bottom of his screen. I wanted to show the last 4 messages at one time and possibly allow the player to look back to see 30-50 messages in a log if they want. To do this I set up and object and an array to push the objects into.
So I set up some variables like this initially...
servermessage: {"color1":"yellow", "color2":"white", "message1":"", "message2":""},
servermessagelist: new Array(),
and when I use this command (below) multiple times with different data called by an event by manipulating servermessage.color1 ... .message1 etc...
servermessagelist.push(servermessage)
it overwrites the entire array with copies of that data... any idea why or what I can do about it.
So if I push color1 "RED" and message1 "Rover".. the data is correct then if I push
color1"yellow" and message1 "Bus" the data is two copies of .color1:"yellow" .message1:"Bus"
When you push servermessage into servermessagelist you're really (more or less) pushing a reference to that object. So any changes made to servermessage are reflected everywhere you have a reference to it. It sounds like what you want to do is push a clone of the object into the list.
Declare a function as follows:
function cloneMessage(servermessage) {
var clone ={};
for( var key in servermessage ){
if(servermessage.hasOwnProperty(key)) //ensure not adding inherited props
clone[key]=servermessage[key];
}
return clone;
}
Then everytime you want to push a message into the list do:
servermessagelist.push( cloneMessage(servermessage) );
When you add the object to the array, it's only a reference to the object that is added. The object is not copied by adding it to the array. So, when you later change the object and add it to the array again, you just have an array with several references to the same object.
Create a new object for each addition to the array:
servermessage = {"color1":"yellow", "color2":"white", "message1":"", "message2":""};
servermessagelist.push(servermessage);
servermessage = {"color1":"green", "color2":"red", "message1":"", "message2":"nice work"};
servermessagelist.push(servermessage);
There are two ways to use deep copy the object before pushing it into the array.
1. create new object by object method and then push it.
servermessagelist = [];
servermessagelist.push(Object.assign({}, servermessage));
Create an new reference of object by JSON stringigy method and push it with parse method.
servermessagelist = [];
servermessagelist.push(JSON.parse(JSON.stringify(servermessage));
This method is useful for nested objects.
servermessagelist: new Array() empties the array every time it's executed. Only execute that code once when you originally initialize the array.
I also had same issue. I had bit complex object that I was pushing in to the array. What I did; I Convert JSON object as String using JSON.stringify() and push in to the Array.
When it is returning from the array I just convert that String to JSON object using JSON.parse().
This is working fine for me though it is bit far more round solution.
Post here If you guys having alternative options
I do not know why a JSON way of doing this has not been suggested yet.
You can first stringify the object and then parse it again to get a copy of the object.
let uniqueArr = [];
let referencesArr = [];
let obj = {a: 1, b:2};
uniqueArr.push(JSON.parse(JSON.stringify(obj)));
referencesArr.push(obj);
obj.a = 3;
obj.c = 5;
uniqueArr.push(JSON.parse(JSON.stringify(obj)));
referencesArr.push(obj);
//You can see the differences in the console logs
console.log(uniqueArr);
console.log(referencesArr);
This solution also work on the object containing nested keys.
Before pushing, stringify the obj by
JSON.stringify(obj)
And when you are using, parse by
JSON.parse(obj);
As mentioned multiple times above, the easiest way of doing this would be making it a string and converting it back to JSON Object.
this.<JSONObjectArray>.push(JSON.parse(JSON.stringify(<JSONObject>)));
Works like a charm.

Deserializing JavaScript object instance

I am working on an app that heavily uses JavaScript. I am attempting to include some object-oriented practices. In this attempt, I have created a basic class like such:
function Item() { this.init(); }
Item.prototype = {
init: function () {
this.data = {
id: 0,
name: "",
description: ""
}
},
save: function() {
alert("Saving...");
$.ajax({
url: getUrl(),
type: "POST",
data: JSON.stringify(this.data),
contentType: "application/json"
});
}
}
I am creating Item instances in my app and then saving them to local storage like such:
Item item = new Item();
window.localStorage.setItem("itemKey", JSON.stringify(item));
On another page, or at another time, I am retriving that item from local storage like such:
var item = window.localStorage.getItem("itemKey");
item = JSON.parse(item);
item.save();
Unfortunately, the "save" function does not seem to get reached. In the console window, there is an error that says:
*save_Click
(anonymous function)
onclick*
I have a hunch that the "(anonymous function)" is the console window's way of saying "calling item.save(), but item is an anonymous type, so I am trying to access an anonymous function". My problem is, I'm not sure how to convert "var item" into an Item class instance again. Can someone please show me?
Short answer:
Functions cannot be serialized into JSON.
Explanation:
JSON is a cross-platform serialization scheme based on a subset of JS literal syntax. This being the case, it can only store certain things. Per http://www.json.org/ :
Objects: An object is an unordered set of name/value pairs. An object begins with { (left brace) and ends with } (right brace). Each name is followed by : (colon) and the name/value pairs are separated by , (comma).
Arrays: An array is an ordered collection of values. An array begins with [ (left bracket) and ends with ] (right bracket). Values are separated by , (comma).
values: A value can be a string in double quotes, or a number, or true or false or null, or an object or an array. These structures can be nested.
Functions cannot be serialized into JSON because another non-JS platform would not be able to unserialize and use it. Consider the example in reverse. Say I had a PHP object at my server which contained properties and methods. If I serialized that object with PHP's json_encode() and methods were included in the output, how would my JavaScript ever be able to parse and understand PHP code in the methods, let alone use those methods?
What you are seeing in your resulting JSON is the toString() value of the function on the platform you're using. The JSON serilizer calls toString() on anything being serialized which isn't proper for JSON.
I believe your solution is to stop storing instances in JSON/local storage. Rather, save pertinent data for an instance which you set back to a new instance when you need.
I know this question is answered already, however I stumbled upon this by accident and wanted to share a solution to this problem, if anyone is interested.
instead of doing this:
var item = window.localStorage.getItem("itemKey");
item = JSON.parse(item);
item.save();
do something like this:
// get serialized JSON
var itemData = window.localStorage.getItem("itemKey");
//instantiate new Item object
var item = new Item();
// extend item with data
$.extend(item, JSON.parse(itemData));
// this should now work
item.save();
this will work so long as the function you are wanting to call (ie, save()) is prototypal and not an instance method (often times the case, and is indeed the case in the OP's original question.
the $.extend method is a utility method of jquery, but it is trivial to roll your own.
You cant do that, how can javascript possibly knows that item have a save function ? json doesnt allow functions as datas. just read the json spec , you cant save functions.
what you need to do is to create a serialize and deserialize method in the hash you want to stock. that will specifiy what to export and how you can "wake up" an object after parsing the corresponding json string.
You can only store plain Objects in DOMstorages (cookies, urlparams..., everything that needs [de]serialisation through JSON.stringify/JSON.parse). So what you did when sending the ajax data
ajaxsend(this.data);
also applies to string serialisation. You can only store the data, not the instance attributes (like prototype, constructor etc.). So use
savestring(JSON.stringify(item.data));
which is possible because item.data is such a plain Object. And when restoring it, you will only get that plain data Object back. In your case it's easy to reconstruct a Item instance from plain data, because your Items hold their values (only) in a public available property:
var item = new Item;
item.data = JSON.parse(getjsonstring());
Disclaimer
Not a full time time J.S. Developer, answer may have some minor bugs:
Long Boring Explanation
As mentioned by #JAAulde, your object cannot be serialized into JSON, because has functions, the technique that you are using doesn't allow it.
Many people forget or ignore that the objects that are used in an application, may not be exactly the same as saved / restored from storage.
Short & quick Answer
Since you already encapsulate the data members of your object into a single field,
you may want to try something like this:
// create J.S. object from prototype
Item item = new Item();
// assign values as you app. logic requires
item.data.name = "John Doe";
item.data.description = "Cool developer, office ladies, love him";
// encoded item into a JSON style string, not stored yet
var encodedItem = JSON.stringify(item.data)
// store string as a JSON string
window.localStorage.setItem("itemKey", encodedItem);
// do several stuff
// recover item from storage as JSON encoded string
var encodedItem = window.localStorage.getItem("itemKey");
// transform into J.S. object
item.data = JSON.parse(encodedItem);
// do other stuff
Cheers.

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