Tuesday, October 15, 2024

UW JS 310 Aut 24 Class 2 notes 15-OCT-2024

Objects are complex data type

Const myObj = {};

console.log(myObj);


const person = {

firstName : ‘S’,

lastName: ‘Man’,

Age: 4

}


person.lastName = ‘Johnson’;

person.numberOfGuitars = 3;

console.log(person);


Objects destructuring : assigning properties of an object to individual variables 

const {firstName, age} = person;

console.log(“ghost emoji”, firstName, age);


Consider this example

const person = {

‘First Name’ : ‘S’,

lastName: ‘Man’,

Age: 40

}


To get the ‘First Name’ we have to do this:

person.[‘First Name’]

Also object keys should be strings, the values can be anything


Q) why does the index start with zero in javascript?

A: This one’s rooted in the history of computer science. Zero-based indexing traces

back to the C programming language, created in the early '70s. Arrays in C are

designed to start at the beginning of a memory block, and indexing from zero

simplifies the computation of an element’s address. JavaScript inherits many conventions

from C, including zero-based indexing. Once this became standard, many languages

that came afterward stuck with it to keep things consistent and predictable.

It's a nod to the past that still makes sense in today's coding world. 


array.pop() - removes the last value and 

array.push() - adds a value at the end of an array

array.concat() - takes 2 arrays and merge it to 1 array

array.slice()


Destructuring an array

const arr = [‘apple’,’orange’,’banana’];

const [first,second,third] = arr;

console.log(first); // apple


Array can be multi dimensional, can be array of arrays

const arr=[[1,2,3], [4,5,6], [7,8,9]];

console.log(arr[1][2]); // 6


const arr=[[1,2,3], [4,[‘a’,’b’,’v’],6], [7,8,9]];


Reference vs primitive data types :

Reference types are like class and arrays, when copies are made reference are copied

Primitives are like string, numbers, booleans, when copies are made values are copied

const name = ‘james’;

const firstName = name;

console.log(firstName);


Easy way to know is if we make a copy and cannot change the value then it is primitives

type when we precede with ‘const’

Eg of reference type variables

const arr=[1,2,3]

const narr = arr

arr[1] = 5

console.log(arr) // [1,5,3]

console.log(narr) // [1,5,3]




Spread operators (...) are incredibly handy in JavaScript! They allow you to easily expand elements of an array or object. 

When it comes to arrays, you can use them to create a new array that includes elements from an existing array. For example:


const arr1 = [1, 2, 3];

const arr2 = [...arr1, 4, 5, 6];

const arr3 = [...arr2] // copy by value

const arr4 = arr3 // copy by reference

console.log(arr2); // Output: [1, 2, 3, 4, 5, 6]


const arr2 = [ 4, 5, 6,...arr1];

const arr2 = [ 4, 5,...arr1,6];


You can also use them for copying arrays, combining arrays, and even spreading elements as function arguments. 


object copy by value, using spread operator

const billRodgersIV={...willRodgersIII} 


const russell = {

touchdowns:2,

yards:1123,

sacks:4

}


copy other values as is but changed the touchdowns value to 5

const russellWeek17 = {

...russell,

touchdowns:5,

interceptions : 1234 // and adding new properties like this

}


RegEx : way of validation of input from user 


Quiz notes :


In JavaScript, null and undefined don't have properties. Here's why:

Null: Represents the intentional absence of any object value. It's like a placeholder to say
"there's no value here." Since it signifies the absence of an object, it naturally doesn't have
properties or methods.
Undefined: Indicates a variable that hasn't been assigned a value yet.
It's the default value for uninitialized variables, and since it means "no value yet,"

it doesn't have properties either.

On the other hand, numbers, strings, and arrays do have properties and methods. Numbers and strings have

built-in methods (like .toFixed() for numbers or .length for strings), and arrays are objects in JavaScript,

so they come packed with a host of properties and methods.


 dot notation and bracket notation are the right ways to access properties in JavaScript objects.

Dot notation is simple and straightforward: object.property

Bracket notation allows for dynamic property access, where the property name is specified as a
string: object["property"]

Arrow notation isn’t a thing when accessing object properties. It’s actually used for functions and doesn’t

relate to property access.


Saturday, May 16, 2020

Node.JS rest api Tutorials


Install appropriate node version from here : 
https://nodejs.org/en/download/

All these commands must be run on command prompt after npm package 
installation.
generate an empty npm project without going through an interactive 
process.
npm init -y

install required (driver) packages
npm i express mysql body-parser cors 

install nodemon, it is a tool that helps by automatically restarting 
the node 
application when file changes in the directory are detected
npm i -g nodemon




//First create a folder (lers say "nodejs-rest-api")
// and then create a file in that folder called "app.js" 
//and you should add this code :

var express = require("express");
var app = express();
// mysql driver
var mysql = require("mysql");
// parser to parse POST body content
var bodyParser = require("body-parser");
// this is the port where your application will run (eg: localhost:9800)
var port = 9800;

// create connection object for database
let connection = mysql.createConnection({
    host: "localhost",
    user: "user",
    password: "password",
    database: "somedatabase",
});

app.use(bodyParser.json()); // so it can support JSON-encoded bodies
app.use(
    bodyParser.urlencoded({
        // so it can support URL-encoded bodies
        extended: true,
    })
);

// this will connect MySQL
connection.connect();

// this will create a get request with route "localhost:9800/"
// req -> request
// res -> response
app.get("/", (req, res) => {
    res.send("Application started");
});

// this will create a get request with route "localhost:9800/coaches"
app.get("/coaches", (req, res) => {
    connection.query("SELECT * FROM coachmain;", (err, result) => {
        if (err) {
            console.log(err);
            res.json({ error: true });
        } else {
            console.log(result);
            res.json(result);
        }
    });
});

// this will create a delete request with route "localhost:9800/deleteCoach"
/*
delete body should be something like this :
    {
        "coachId": 1
    }
*/
app.delete("/deleteCoach", function (req, res) {
    // get data from forms and add to the table called coachmain
    var coachId = parseInt(req.body.coachId);
    var queryString =
        `DELETE FROM  coachmain 
           where coachId =
                '` +
        coachId +
        `'`;
    connection.query(queryString, function (err, result) {
        if (err) {
            // handle error and notify user
            res.status(400).send(err);
        } else {
            // success message here. if you forget this, 
            // the request will wait till timeout
            res.status(201).send(req.body);
        }
    });
});

// this will create a post request with route "localhost:9800/deleteCoach"
/*
post body should be something like this :
    {
        "name": "full name",
        "coachId": 1,
        "season": 2
    }
*/
app.post("/newCoach", function (req, res) {
    // get data from forms and add to the table called user..
    var name = req.body.name;
    var coachId = parseInt(req.body.coachId);
    var season = parseInt(req.body.season);
    var queryString =
        `INSERT INTO coachmain 
            (
                name, coachId, season
            )
            VALUES
            (
                '` +
        name +
        `','` +
        coachId +
        `','` +
        season +
        `'
            )`;
    connection.query(queryString, function (err, result) {
        if (err) {
            // handle error and notify user
            res.status(400).send(err);
        } else {
            // success message here. if you forget this, 
            // the request will wait till timeout
            res.status(201).send(req.body);
        }
    });
});

// application will listen to this port
app.listen(port, (err) => {
    console.log("running on :" + port);
});

Tuesday, May 12, 2020

Create Software Inventories

# read all child keys (*) from all four locations and do not emit # errors if one of these keys does not exist Get-ItemProperty -Path 'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*', 'HKLM:\SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Uninstall\*', 'HKCU:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*', 'HKCU:\SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Uninstall\*' -ErrorAction Ignore | # list only items with the DisplayName Where-Object DisplayName | # show these registry values per item Select-Object -Property DisplayName, DisplayVersion, UninstallString, InstallDate | # sort by DisplayName Sort-Object -Property DisplayName

taken from :

https://community.idera.com/database-tools/powershell/powertips/b/tips/posts/create-software-inventories

Monday, January 27, 2020

Tuesday, September 24, 2019

various sql utility t-sql

-- content of store procedure 
sp_helptext 'dbo.proc_name'

-- which store procedure ran and when
 SELECT DB_NAME(database_id)
    ,OBJECT_NAME(object_id,database_id)
    ,cached_time
    ,last_execution_time
    ,execution_count
FROM sys.dm_exec_procedure_stats order by last_execution_time DESC

-- search for stored proc which contains text you are searching for
SELECT ROUTINE_NAME, ROUTINE_DEFINITION
    FROM INFORMATION_SCHEMA.ROUTINES 
    WHERE ROUTINE_DEFINITION  LIKE '%your search text%' 
    AND ROUTINE_TYPE='PROCEDURE'


-- find tables in database which matches our criteria
DECLARE @SelectCol1     nvarchar(60)
insert into @tblNames (name)
SELECT name FROM sys.databases
where name like '0r'
How to enable cdc : record keeping in database 
use master go select [name], database_id, is_cdc_enabled from sys.databases go  use [databasename] go exec sys.sp_cdc_enable_db go
 select * from [dbname].[dbo].[tblMain]

--  ALTER TABLE [dbname].[dbo].[tblMain] ADD [colName] bigint; --add column

Tuesday, July 7, 2015

KMP algorithm

IndexOf Implementation :-

public static int[] FailureFunction(string p)
        {
            int[] F = new int[p.Length];
            F[0] = 0;
            int i = 1, j = 0;
            while (i < F.Length)
            {
                if (p[i] == p[j])
                {
                    F[i] = j + 1;
                    i++;
                    j++;
                }
                else if (j > 0)
                {
                    j = F[j - 1];
                }
                else
                {
                    F[i] = 0;
                    j++;
                }
            }
            return F;
        }

        public static int KMP(string s, string p)
        {
            int[] F = FailureFunction(p);
            int i = 0, j = 0;
            while (i < s.Length)
            {
                if (s[i] == p[j])
                {
                    if (j == p.Length-1)
                    {
                        return i - j;//match
                    }
                    else
                    {
                        i++; j++;
                    }
                }
                else
                {
                    if (j > 0)
                    {
                        j = F[j - 1];
                    }
                    else
                    {
                        i++;
                    }
                }

            }
            return -1;
        }