Month: June 2017
MONGODB: What is a projection?
A projection is when you search for documents in MongoDB but only get back the fields that you request.
example records {name: “Tom”, age: “35”, zipcode: “10003”,_id:778789754}
using projection for name and zipcode: {name: “Tom”, zipcode: “10003”}
var mongo = require(“mongodb”).MongoClient;
var url = “mongodb://localhost/addressbook”;
var collectionName = “friends”;
mongo.connect(url,function(err,db){
if(err) console.log(err)//throw err;
else{
var collection = db.collection(collectionName);
collection.find({},{name: 1, age: 0,_id:0,zipcode: 0}).toArray( function(err,documents){
if(err) console.log(err)//throw err;
else{
console.log(documents)
}
});
db.close();
}
})
node notes: require() caches module.exports
if you are importing a file that instantiates a new object
when you import the file again as a 2nd object you would expect … a new object
but your 2nd variable will be the same object as the first variable, even though a “new” constructor was used. why?
Node caches module imports , it wont load the file again so no new instance!!!
example:
Node notes : on require with no js file in local path
if you require, for example “greet”, and greet.js is not found, node will look for folder called “greet” and then look for a file called index.js
Ubuntu: Install Visual Studio Code via apt-get
Why fiddle with downloading from the browser when apt-get will do?
sudo add-apt-repository -y "deb https://packages.microsoft.com/repos/vscode stable main"
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys EB3E94ADBE1229CF
sudo apt update
sudo apt -y install codeIf need upgrade
sudo apt -y upgrade
sudo apt -y dist-upgradegreat answer from zurfyx
https://askubuntu.com/questions/616075/how-do-i-install-visual-studio-code
Errors encountered on my way to install Node.JS v8 on ubuntu
when running apt-get install nodejs
You might want to run ‘apt-get -f install’ to correct these:
The following packages have unmet dependencies:
libgail-3-0 : Depends: libgtk-3-0 (= 3.20.9-1ubuntu2) but 3.18.9-1ubuntu4 is to be installed
nodejs : Depends: libuv1 (>= 1.6.1) but it is not going to be installed
python3-gi-cairo : Depends: python3-gi (= 3.22.0-1) but 3.20.0-0ubuntu1 is to be installed E: Unmet dependencies. Try ‘apt-get -f install’ with no packages (or specify a solution).
to fix: apt-get -f install
When trying to install nodejs again will only allow for node-legacy (v4)
to fix:
# Using Ubuntu curl -sL https://deb.nodesource.com/setup_8.x | sudo -E bash - sudo apt-get install -y nodejs
finally at v8 locally
io.emit vs socket.emit
io.emit lets the server send an event to all the connected clients at once. This is useful when you need to send some data to everyone. This is something we want everyone to be able to see.
socket.emit sends an event to a single socket. This is great when you need to send an event to a single user. Example: This is why we use socket.emit when sending out a greeting message. It only needs to go to that one user.
socket.io notes
JavaScript Classes review
Some basic notes
// *****START CLASS***********************************************
//The constructor function is called automatically when an instance of the class is created.
// a special method for creating and initializing an object created with a class.
// There can only be one special method with the name “constructor” in a class.
class Person {
constructor (name,age) { //this is a function
// console.log(name,age)
this.name=name;
this.age=age;
}
//methods
getUserDescription(){return `${this.name} is ${this.age} year(s) old`}
}
// *****END CLASS***********************************************
var me = new Person(“Andrew”,25); //arguments are passed to constructor function
// console.log(“this.name”, me.name)
// console.log(“this.age”, me.age)
var description = me.getUserDescription(); // Andrew is 25 year(s) old
console.log(description);
Location object
Contains info about the URL
Part of the window object, also accessible by document object
Can access in dev tools by typing location
Items in location
- search. : that is the query string
- pathname
- origin
- href
- port
See MDN for more
Examples: access seatch use window.location.search
See stevenbenner jQuery deparam for deconstruction of params or go here
Example deparam after loading function
JQuery.deparam(window.location.search)
Continuous posting on blog
Was watching a YouTube video by simple programmer where he pointed out that one should keep blogging and putting down their thoughts. It shows that you have been working on a particular tech.
That’s was a good point. It reinforces your own learning and can help others who are also looking for information. When I was learning VMware I wrote tons of articles that were used by others. I would even surprise myself and find my own articles when looking for an answer.
Downloaded the WordPress app and will arrive for more as we all should
vSPARROW 