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How do I call a method to an object?

How would I call my method to my other objects?
Been having lots of trouble with everything I've tried.
I'm not that confident with this stuff, just looking on how to tell if the object is safe to drive or not.
//Create a constructor function called `Track`. It will accept two parameters - the name of the track and the maximum capacity of the track.
let track = function(name, capacity){
this.trackName=name
this.personnel=0;
this.cars=[];
this.cap=capacity;
}
//We'll need a value for the average weight of a person but this value will be the same for all tracks.
//Add a property `personWeight` on the `Track` prototype so that all instances share the same value.
track.prototype.personWeight = 200
//Create three methods on the prototype that will calculate track weight, person weight, and if its safe to drive
function personWeight(){
personnelWeight = this.personWeight * this.personnel
return personnelWeight
}
function trackWeight(){
let carsTotal = function myFunc(total, num) {
return total - num;
}
let weightTotal = (this.personnel * this.personWeight) + (this.carsTotal)
return weightTotal
}
function safeToDrive(){
if(this.trackWeight<this.capacity){
return true
}
}
//Create two track objects
let trackOne = new track ("Daytona", 25000);
trackOne.cars = [1800, 2400, 2700, 3200, 3600, 3800, 4200]
trackOne.personnel = 10
let trackTwo = new track ("Indiana",15000);
trackTwo.cars = [2000, 2300, 2800, 3000, 3500, 3700, 4000]
trackTwo.personnel = 8
//Call the `safeToDrive` method for truck objects.

With the code as it is now, you would use safeToDrive.call(trackOne). However, this is not the straight-forward way you would do it normally.
I guess what you really want is assigning these methods to the prototype:
track.prototype.safeToDrive = function () {
if(this.trackWeight<this.capacity){
return true
}
}
Then you'd call them using trackOne.safeToDrive().
The same goes for personWeight and trackWeight.
A few other observations:
Your check for this.capacity won't work because the property is actually called cap and not capacity according to what you set in your constructor.
safeToDrive currently returns true or nothing, i.e. undefined, and not true or false as you would expect.
You could fix that by either adding an else with return false or simply using return this.trackWeight < this.capacity instead of the whole if condition.
Oh, also, your personnelWeight variable is accidentally made global. Add a let before it. To avoid this in the first place, add 'use strict' at the top of your file to get warned about this issue next time.
I'm not sure what you are doing with carsTotal there though, I guess that should be a member function as well (otherwise you couldn't even call it using this.carsTotal as you do now). Plus, your indention is wrong there. (Put your file through a beautifier to see what I mean.)
Do you mean truck instead of track maybe...?

Why is the value of a specific key for a doc getting 'undefined' [duplicate]

Is there something that I'm missing that would allow item to log as an object with a parameter, but when I try to access that parameter, it's undefined?
What I've tried so far:
console.log(item) => { title: "foo", content: "bar" } , that's fine
console.log(typeof item) => object
console.log(item.title) => "undefined"
I'll include some of the context just in case it's relevant to the problem.
var TextController = function(myCollection) {
this.myCollection = myCollection
}
TextController.prototype.list = function(req, res, next) {
this.myCollection.find({}).exec(function(err, doc) {
var set = new Set([])
doc.forEach(function(item) {
console.log(item) // Here item shows the parameter
console.log(item.title) // "undefined"
set.add(item.title)
})
res.json(set.get());
})
}
Based on suggestion I dropped debugger before this line to check what item actually is via the node repl debugger. This is what I found : http://hastebin.com/qatireweni.sm
From this I tried console.log(item._doc.title) and it works just fine.. So, this seems more like a mongoose question now than anything.
There are questions similar to this, but they seem to be related to 'this' accessing of objects or they're trying to get the object outside the scope of the function. In this case, I don't think I'm doing either of those, but inform me if I'm wrong. Thanks

Solution
You can call the toObject method in order to access the fields. For example:
var itemObject = item.toObject();
console.log(itemObject.title); // "foo"
Why
As you point out that the real fields are stored in the _doc field of the document.
But why console.log(item) => { title: "foo", content: "bar" }?
From the source code of mongoose(document.js), we can find that the toString method of Document call the toObject method. So console.log will show fields 'correctly'. The source code is shown below:
var inspect = require('util').inspect;
...
/**
* Helper for console.log
*
* #api public
*/
Document.prototype.inspect = function(options) {
var isPOJO = options &&
utils.getFunctionName(options.constructor) === 'Object';
var opts;
if (isPOJO) {
opts = options;
} else if (this.schema.options.toObject) {
opts = clone(this.schema.options.toObject);
} else {
opts = {};
}
opts.minimize = false;
opts.retainKeyOrder = true;
return this.toObject(opts);
};
/**
* Helper for console.log
*
* #api public
* #method toString
*/
Document.prototype.toString = function() {
return inspect(this.inspect());
};

Make sure that you have defined title in your schema:
var MyCollectionSchema = new mongoose.Schema({
_id: String,
title: String
});

Try performing a for in loop over item and see if you can access values.
for (var k in item) {
console.log(item[k]);
}
If it works, it would mean your keys have some non-printable characters or something like this.
From what you said in the comments, it looks like somehow item is an instance of a String primitive wrapper.
E.g.
var s = new String('test');
typeof s; //object
s instanceof String; //true
To verify this theory, try this:
eval('(' + item + ')').title;
It could also be that item is an object that has a toString method that displays what you see.
EDIT: To identify these issues quickly, you can use console.dir instead of console.log, since it display an interactive list of the object properties. You can also but a breakpoint and add a watch.

Use findOne() instead of find().
The find() method returns an array of values, even if you have only one possible result, you'll need to use item[0] to get it.
The findOne method returns one object or none, then you'll be able to access its properties with no issues.

Old question, but since I had a problem with this too, I'll answer it.
This probably happened because you're using find() instead of findOne(). So in the end, you're calling a method for an array of documents instead of a document, resulting in finding an array and not a single document. Using findOne() will let you get access the object normally.

A better way to tackle an issue like this is using doc.toObject() like this
doc.toObject({ getters: true })
other options include:
getters: apply all getters (path and virtual getters)
virtuals: apply virtual getters (can override getters option)
minimize: remove empty objects (defaults to true)
transform: a transform function to apply to the resulting document before returning
depopulate: depopulate any populated paths, replacing them with their original refs (defaults to false)
versionKey: whether to include the version key (defaults to true)
so for example you can say
Model.findOne().exec((err, doc) => {
if (!err) {
doc.toObject({ getters: true })
console.log('doc _id:', doc._id) // or title
}
})
and now it will work

You don't have whitespace or funny characters in ' title', do you? They can be defined if you've quoted identifiers into the object/map definition. For example:
var problem = {
' title': 'Foo',
'content': 'Bar'
};
That might cause console.log(item) to display similar to what you're expecting, but cause your undefined problem when you access the title property without it's preceding space.

I think using 'find' method returns an array of Documents.I tried this and I was able to print the title
for (var i = 0; i < doc.length; i++) {
console.log("iteration " + i);
console.log('ID:' + docs[i]._id);
console.log(docs[i].title);
}

If you only want to get the info without all mongoose benefits, save i.e., you can use .lean() in your query. It will get your info quicker and you'll can use it as an object directly.
https://mongoosejs.com/docs/api.html#query_Query-lean
As says in docs, this is the best to read-only scenarios.

Are you initializing your object?
function MyObject()
{
this.Title = "";
this.Content = "";
}
var myo1 = new MyObject();
If you do not initialize or have not set a title. You will get undefined.

When you make tue query, use .lean() E.g
const order = await Order.findId("84578437").lean()

find returns an array of object , so to access element use indexing, like
doc[0].title

ReactJS: Join map output with concatenating value

In my ReactJS application I am getting the mobile numbers as a string which I need to break and generate a link for them to be clickable on the mobile devices. But, instead I am getting [object Object], [object Object] as an output, whereas it should be xxxxx, xxxxx, ....
Also, I need to move this mobileNumbers function to a separate location where it can be accessed via multiple components.
For example: Currently this code is located in the Footer component and this code is also need on the Contact Us component.
...
function isEmpty(value) {
return ((value === undefined) || (value === null))
? ''
: value;
};
function mobileNumbers(value) {
const returning = [];
if(isEmpty(value))
{
var data = value.split(',');
data.map((number, index) => {
var trimed = number.trim();
returning.push(<NavLink to={`tel:${trimed}`} key={index}>{trimed}</NavLink>);
});
return returning.join(', ');
}
return '';
};
...
What am I doing wrong here?
Is there any way to create a separate file for the common constants / functions like this to be accessed when needed?

First question:
What am I doing wrong here?
The issue what you have is happening because of Array.prototype.join(). If creates a string at the end of the day. From the documentation:
The join() method creates and returns a new string by concatenating all of the elements in an array (or an array-like object), separated by commas or a specified separator string. If the array has only one item, then that item will be returned without using the separator.
Think about the following:
const navLinks = [{link:'randomlink'}, {link:'randomlink2'}];
console.log(navLinks.join(','))
If you would like to use concatenate with , then you can do similarly like this:
function mobileNumbers(value) {
if(isEmpty(value)) {
const data = value.split(',');
return data.map((number, index) => {
const trimed = number.trim();
return <NavLink to={`tel:${trimed}`} key={index}>{trimed}</NavLink>;
}).reduce((prev, curr) => [prev, ', ', curr]);
}
return [];
};
Then you need to use map() in JSX to make it work.
Second question:
Is there any way to create a separate file for the common constants / functions like this to be accessed when needed?
Usually what I do for constants is that I create in the src folder a file called Consts.js and put there as the following:
export default {
AppLogo: 'assets/logo_large.jpg',
AppTitle: 'Some app name',
RunFunction: function() { console.log(`I'm running`) }
}
Then simply import in a component when something is needed like:
import Consts from './Consts';
And using in render for example:
return <>
<h1>{Consts.AppTitle}</h1>
</>
Similarly you can call functions as well.
+1 suggestion:
Array.prototype.map() returns an array so you don't need to create one as you did earlier. From the documentation:
The map() method creates a new array populated with the results of calling a provided function on every element in the calling array.
I hope this helps!

Finding elements in an array of objects where you have a bigger key

I'm writing a tiny reactive framework where I need to find out which subscriber needs updating. I'm implementing deep binding and I'm running into a wall how to find subscribers in an effective manner.
A stored variable can be an object, so for example
{
"user": {
"preferences": {
"food": "vegetarian"
}
}
}
You can get content to any level of this variable like this
getVar("user_preferences_food");
getVar("user_preferences");
However, you can also update it like that
setVar("user_preferences_food", "meat");
setVar("user_preferences", {"food": "meat"});
But in case of the first setVar (user_preferences_food) how can I find the subscriber using getVar("user_preferences"); or even getVar("user"); most effectively.
I already got it working by splitting the var on _ and then one by one concatting the next level and merging all the resulting arrays. But this is very resource intensive. Especially if there are a lot of subscribers. There must be a better way to find them that is less resource intensive.
Edit: I left out part of the explanation.
There is a subscribe method too
subscribe("user", cb);
subscribe("user_preferences", cb);
subscribe("user_preferences_food", cb);
These subscriptions are stored in an array in the framework.
As soon as "user_preferences_food" is updated for example, all subscriptions above should be triggered. But obviously not subscribe('othervar');
simplification of the subscribe method:
var subscriptions = [];
function subscribe(var, callback){
subscriptions.push({var: var, cb: callback});
}
Simplification of getVar
vars = {};
getVar(var){
// find var in vars with this logic: https://stackoverflow.com/a/18937118/249710
// current exact match on subscribers, but need the "parents, grandparents etc here
var toUpdate = _.where(subscriptions, {
"var" : var
});
_.each(toUpdate, function(sub){ sub.cb();});
}
Storing or getting data as part of the key I've already got covered. It is just finding the subscribers in the most effective manner
ps: this is in an environment where I cannot rely on ES6 yet (not all users have it enabled), there is no DOM but I do have underscore included. (Titanium app development platform)

I would try to make a list for the callbacks, so you loop trough one list so you dont have to search, because you know the list is there with all the callbacks.
So if you call setVar('user_prefs') you set a seperate list with the root var. in this case its the user.
if any object is changed with setVar (in depth or not) you go to you're root var, get the list and loop trough this list with the callbacks.
The beauty of this is you can set a list with the root var,
var cbList[FIRSTVAR] this contains all the callbacks. No searching just loop.
Its the mongoDb principle, the data is ready to go, you don't search because you know the list is already there.

You could split the string and use it for reduceing the object.
function getVar(object, path) {
return path
.split('_')
.reduce(function (o, k) {
return (o || {})[k];
}, object);
}
function setVar(object, path, value) {
var keys = path.split('_'),
last = keys.pop();
keys.reduce(function (o, k) {
return o[k] = o[k] || {};
}, object)[last] = value;
}
var object = { user: { preferences: { food: "vegetarian" } } };
console.log(getVar(object, "user_preferences_food"));
console.log(getVar(object, "user_preferences"));
setVar(object, "user_preferences_food", "meat");
console.log(object);
setVar(object, "user_preferences", {"food": "meat"});
console.log(object);
.as-console-wrapper { max-height: 100% !important; top: 0; }

I ended up doing this:
var options = [];
var parts = key.split('_');
var string = parts[0];
_.each(parts, function(p, i){
if (i > 0) string += '_' + p;
options.push(string);
});
var toUpdate = _.filter(subscribers, function(sub){
if (sub.var.indexOf(key + '_') === 0) return true;
if (options.indexOf(sub.var) > -1) return true;
return false;
});
So checking with indexOf on the string to see if there are children. And building an array with parents so any layer is a match, and doing an indexOf on that as well. I think this is the least complicated method of implementing it

Array.slice() parameter is not a function

Im encountering an odd problem when going through freeCodeCamp beta.
The "purpose" of this is not modifying the original array and using functional programming techniques to modify arrays.
However I keep getting complaints about the "array" parameter is the remove function not being a valid function:
// the global variable
var bookList = [
"The Hound of the Baskervilles",
"On The Electrodynamics of Moving Bodies",
"Philosophiæ Naturalis Principia Mathematica",
"Disquisitiones Arithmeticae"];
/* This function should add a book to the list and return the list */
// New parameters should come before the bookName one
// Add your code below this line
function add (bookListTemp, bookName) {
let newBookArr = bookListTemp;
return newBookArr.push(bookName);
// Add your code above this line
}
/* This function should remove a book from the list and return the list */
// New parameters should come before the bookName one
// Add your code below this line
function remove (bookList,bookName) {
let newArr = bookList.slice();
if (newArr.indexOf(bookName) >= 0) {
return newArr.slice(0, 1, bookName);
// Add your code above this line
}
}
var newBookList = add(bookList, 'A Brief History of Time');
var newerBookList = remove(bookList, 'On The Electrodynamics of Moving Bodies');
var newestBookList = remove(add(bookList, 'A Brief History of Time'),
'On The Electrodynamics of Moving Bodies');
console.log(bookList);
In the remove function i've tried taking the parameter and doing array.slice() method as well as array.concat() method. Since doing let newArr = bookList doesn't actually make a new array correct? it just makes a new copy that references the original array correct?
The exact error I get is TypeError: bookList.slice is not a function
What's even weirder is Array.isArray(bookList) returns true (in the function remove. So I don't understand why it's complaining about array methods?

Your problem is Array.push
return The new length property of the object upon which the method was
called.
You should return array instead
function add (bookListTemp, bookName) {
let newBookArr = bookListTemp;
newBookArr.push(bookName);
// Add your code above this line
return newBookArr;
}
OR
Let's try Array.concat instead
function add (bookListTemp, bookName) {
let newBookArr = bookListTemp;
return newBookArr.concat(bookName);
// Add your code above this line
}

There are two ways to copy the array without mutating it. You will not be able to use the .slice() method on the bookList, because it is an argument in the function and therefore not an array. The work around is var newBookArr = Array.prototype.slice.call(bookListTemp); or [].slice.call(bookListTemp);
This allows you to perform the slice on the bookList when it is an argument. The other way I discovered, when playing around with it - var newBookArr = [].concat(bookListTemp);
When trying var newBookArr = [].push(bookListTemp); we find the original bookList pushed inside the new array. So it is a copy, but as an array within an array. the .concat() method merges the old array into the new.