Intro to JavaScript Series

• The lecture series is starting a new JavaScript series after the HTML series.
• The speaker acknowledges that learning CSS after HTML is generally a better approach but is prioritizing JavaScript based on a poll.
• CSS content will be supplemented to the channel as supplemental material, but the primary focus will be on the JavaScript series.
• Hesitance has almost a decade of experience teaching and using JavaScript.
• The speaker wants to focus on building confidence in JavaScript for the students

Teaching Philosophy

• Goal is to build Javascript confidence
• Knowing Javascript behind the scenes helps to gain more Javascript perspective
• Hands-on projects contribute to confidence with Javascript
• Real-world application project leads to real Javascript confidence
• Project development can start after learning basic Javascript
• While in-depth knowledge is valuable, project experience is key to confidence and cracking interviews.
• The goal is to enable viewers to say "I know JavaScript well" and be able to tackle projects, even with the need for occasional online research.
• The series will cover modern concepts and best practices in JavaScript coding.
• The speaker wants people to appreciate his work after 2-4 years of posting the videos
• Focus on quality over quantity of videos, no need to rush the content

Series Welcome

• The Javascript series officially begins with the introduction
• The series will focus more on coding, with theory kept concise and relevant.
• Viewers should follow along with the coding examples to grasp the mindset required for learning JavaScript.
• The series will cover setting up the system and different ways to write code.

Differentiating .txt and .js Files

• The speaker creates a new folder named "JS-Hindi" on the desktop for the series.
• The folder creation is regardless of operating system
• .txt files do not execute code unlike .js javascript files
• Source code has special meaning within the system

How Javascript Works

• Syntax is structured and specific.
• Programming languages come with their own extensions.
• The difference between .txt and .js files lies in which file type can be injected into software for execution.
• Software contains compilers and interpreters that understand syntax structures.
• When software sees "console," it knows what to do based on predefined syntax.
• For many years the Javascript software was hidden in browsers
• The presenter will show the current day methods of implementing the Javascript software

Node.js Introduction

• For many years it was taught to add Javascript into HTML files, because the Javascript software was not available so easily
• Now the Javascript software is easily available today
• A software (Node.js) can be implemented into Javascript to run the code similar to setting up the Python Software.
• Javascript is no longer front-end browser coding, but also back-end, mobile, etc.
• The reason for Javascript spread everywhere, is because of Node.js
• Download and install the C, C++ environments to run Javascript

How to Install Javascript Software

• Node.js is the most popular Javascript software
• The python.org software is analogous to the JavaScript software to execute code files.
• Net and Node.js installation assignment = find the lead founder and developer of the software and libraries and post in comments section
• Understanding software founding is important for Javascript
• Download Node.js
• Run the downloaded Node JS .exe file
• Choose current or LTS depending on the type of software project
• Agree with the license and install the software
• A code editor is recommended (VS Code, Sublime Text, etc)

Software and Git

• Code editors help with code writing through color correction, auto indentation etc,
• Javascript code is recognized and executed through key words such as the "console" command.
• View in VS Code to start a terminal to start running the software
• "node -v" shows the current version of the software
• "node <filename.js>" is the format to run a Javascript file
• .txt files cannot be run
• Another simpler method of running the Javascript code will be discussed with another video
• Get familiar with online code execution through GitHub

GitHub and Git Introduction

• This lecture will continue the Javascript series
• In the last lecture the Node.js and VS Code IDE were setup to code Javascript
• There are online execution environments. This is for users that do not have the current computer, a high configuration, etc
• Git is a portfolio website with other features
• More discussion in future videos that include: how Git can be used through command lines, the use of Git for multiple software engineers to collaborate, software versioning, track record and software progress
• We will discuss an easy method to setup an online Node.js and JavaScript execution environment
• Make a GitHub Account
• Paid version of Git is for companies
• The free version of Git is still used today for individual software engineers

How to use GitHub.Dev

• Create a new repository clicking on the "New Repository"
• The New Repository will be named "JS-Hindi"
• The repository will be made public for this tutorial and a README file will be added
• GitHub commands are not needed for this tutorial
• The presented will utilize GitHub as an online environment tool
• Click the code section to acquire the code space
• Code spaces will ultimately be free in the future
• Download the files into VS Code as an alternative solution
• Code spaces will need a VS Code install, and the Node.js software
• Click "File" > "View" > "Command Pallette"
• Type "Container" to use dev configuration files
• Adding dev configuration files will install software quickly
• Type "Node" to search for Node configuration for Javascript
• "Node.js and Javascript" option will make the install of Javascript easy
• It does not matter what the Node version the software has
• Agree and click OK
• Rebuild the software environment with install Javascript
• Rebuilding the machine may take some time

How to check the Javascript version

• The Javascript has been rebuilded
• Inside of folder 01-basics, you can create a new file "test.js"
• "console.log('Hitesh)" should be placed in test.js file
• Start terminal by "View" > "Terminal"
• "node test.js" runs the Javascript code inside of the VS Code terminal
• There will be a third method to use the Git Hub to run Javascript code in the next video
• The initial missing .devcontainer folder issue was resolved by finding the test.js file within the 01-basics folder.
• The files are now available in the repository after pushing.
• Files were tracked for changes using the source control icon in the editor (the 4th icon).
• Changes in the files saved by first adding the files via the plus icon and then pushing it
• The message "container config done" was added.
• Pushing saves all the files.
• The steps are: commit and push.
• Files can be downloaded by clicking on code, then clicking local, then clicking on download zip.
• Code files are stored in a Git repository.
• The speaker will make changes to the devcontainer by configuring a file to increase the font size.
• The configuration file can be copied and pasted into the respository, then committed, and then pushed.
• To save limited free hours from Github, the machine needs to be closed once the work is completed.
• To close the machine, click on the current machine under the Code Spaces area, and then proceed to delete the machine, as this step does not affect the code in any way.
• The user can work both online and offline, but online allows resources to be directly provided.
• Online and offline environments are now both symmetrical and developer friendly.

Introduction to Javascript Series

• Javascript knowledge should be acquired to create web applications that are user-friendly.
• The speaker has an intention to build an e-commerce website and social media website for Javascript,
• During the series, the speaker will take the reader through the journey of programming, and Javascript, rather than basic variables and overused examples.

Variables and Constants

• The first step in creating an e-commerce website would be to have a user register to obtain information such as name, email, city, state, and a unique ID.
• All of the information needs to be stored with a memory space.
• Variable refers to space in memory that code can easily call, get, and put information in.
• A constant is information or code you do not intend to change and do not want to be able to change.

Declaring Variables

• Const is used as a keyword and placed at the start.
• Account ID follows after const.
• Pattern for declaring variables include "AccountID", "accountName" or "account_name".
• Any variable name will work if it is readable.
• Most common programming syntax is camel case, such as AccountID for variable declarations.
• Email address is stored using let and adding a double-quote to each side. Example: "[email protected]".
• Code can be written to store an account password.

Keywords

• Keywords are predefined and tell the compiler what to do, such as const, or function names like console.log.
• Keywords tell the compiler what to do, such as allocating memory for const and let.
• Const states the word is locked and value should not be changed.

Javascript Investigation

• Const can be changed as shown on the right, however this should not be done because the linter catches it
• Console.log allows variables to be printed when coding.
• console.log code can be tabbed to auto complete
• Example code for AccountID is then printed.
• AccountID does not allow modification due to Const keyword, however, the linter displays Account email, password, which allowed modification because of various keywords such as let.
• console.table is another method which takes an array of variable names to print
• Javascript declares variable using LET and WAR
• Javascript does not have an initial scope, which means when there's a password, it will use the prior password. Since Javascript did not use a reliable scope, the password can easily be changed.
• Variables using LET fixes the issue of passwords easily being mixed up in the Javascript code.
• When coding in javascript, it's best to use LET and CONST, and never WAR.
• WAR should be avoided for block scope and functional scope.
• It's important to declare a variable such as "Account State", even without adding a value, as best practice. Then, Javascript will deem the value unassigned.

Summarizing

• Const and Let can be used instead of WAR.
• Work toward a full stack development plan to use Javascript.

"use strict" Directive

• Javascript, especially as found in old books, is different than what modern tools and frameworks output
• "use strict" treats all Javascript code as a newer version.
• There is only one “use strict” - “use no strict” is not availabile. Instead this change needs to be modified by simply not using "use strict."

Alert Statements

• Alert statements, when used, automatically open a new window when the code is run.
• Modern Javascript does not automatically run and trigger the alert statement or window. Instead, Javascript requires usage in HTML in order to trigger and run.
• Please pay attention to whether the guide is working with nodeJS or inside the browser as it affects the validity of javascript.

Coding Best Principles

• Code readibility is the most important in coding as it should be readable and future proof. Being executable is not the only indicator the code quality.
• The use of proper newlines should be used to seperate logical sections during variable declarations
• Automatic code formatting should be done to format as well.
• Extreme code formatting should not be experimented with for the sake of code readability.
• Code formatting programs such as Prettier format to make code more readable.

Javascript Documentation

• Javascript, specifically documentation about alerts, is available in various platforms such as Mozilla.
• Ecma International or TC39 has the standards javascript follows to make it language agnostic. However, this documentation is not easy to read.
• The TC39 includes lexical grammar about: comments, whitespace, and unique characters. Includes specifications for variables, naming, values, and rules.
• The takeaway is there are more than one documentation for javascript, with one by Ecma International that browsers use.

Javascript Data Types

• Example Javascript data types includes global objects, numbers, strings and data.
• Const allows specification of keywords that cannot be changed.
• Let specifies a reserve for the word in memory space to put values that can be changed.
• The variable needs to have a reserved name in memory.
• The name may be added in the same way to add things and remove things. The optimization way storage to save things
• Javascript data types are easily defined

Data type Examples

• Name is a String using " " or ' '
• Age is a numbers without " "
• IsLoggedIn is a Boolean using keyword true or false

Javascript Data Types

• Javascript basic data types: Numbers, BigInt, Boolean, Null, Undefined, Symbol, Objects.
• Number ranges from 2 to the power of 53 to 52 - depending on memory
• If the number value goes beyond Number, there is BigInt for trading, stock values
• Boolean includes simply yes and no. Whether temperature came in or didn't come in. Special value
• Null has many stories behind it, a stand-alone value
• Undefined - if a value is not assigned to a variable, simply undefined. Assigned not valued. It is different than an empty string. Example of not defining a value - const temp. Will cause Javascript error
• Symbol - mostly used for React to identify components and set uniqueness
• Objects - the most common and detailed discussion object

Javascript Investigation

• Data Types method - typeof
• Two common methods: either typeof followed by variable to measure, such as "typeof Age", can also measure like "typeof(Age)"
• Known Javascript issue is the typeof(null) prints object. This is the cause of javascript errors
• The value of undefined can be printed using "typeof(undefined)"
• It is important to check that all variables are correct and of the correct type
• Constant variable assignments can be printed to ensure values and methods for that assignment is properly set
• Please refer to the assignment and github to gain more knowledge

Pushing to Github

• First pushed to get the Datatypes information, then commit
• Push, then commit

Conversion of Data Types

• This file will discuss the conversion of data types, but mainly the problems.

• It is best to use data types that are of the same kinds.

• The value and type of all values should be known before hand to avoid issues.

• The below code takes data and converts into a number type:

  let score = "33"
  let valueInNumber = Number(score)
  

• The importance of checking the data's type is important because there is no guarantee where types come from. Example: request from a backend or frontend.

• Data types are checked to know what the exact type is, or what to do in the event wrong types come.

• Number, when used to convert types, begin with a capital letter.

Investigating Javascript Data Types

• By logging data, the kind of data, and data with mixed types will result in the program treating as a string and error, but still output a type - it is up to developer to prevent this.

• By assigning null on javascript, the function will show "0". In comparison, undefined values in JS will report nan.

• It is important to set numbers that will only be numbers to prevent these issues from causing a program to do odd numbers

• Javascript investigation found that mixing Strings with Numbers to add, results in the same String, while Null becomes 0.

• Code example of Booleans include:

  Let isLoggedIn = 1
  let  BooleanIisLiggedIn = Boolean(isLoggedIn)
  

Data Type Conversion Studies

• The current test states: If you were to convert numbers to booleans:

• If "1", Javascript will render as "true".

• If "0", Javascript will render as "false".

• Empty String "" = false.

• If string exists, then "true".

• You cannot control which variable value will prevail over another.

• Conclusion: It’s beneficial to ensure Types are correct before runtime.

• To convert number into string is as easy as invoking String with a capitol “S”, similar to Number and Boolean. Just wrap around a String keyword like the line below.

  sumNumber = 33
  StringNumber = String(numNumber)
  

• It is good to use Javascript, but important to know which Data Types to expect. Convert to proper Type.

• Conversion has several ways to occur - from Number Boolean or String - so important to keep testing and ensure its functionality is working.

Data Conversions and Notes on Data Types

• Conversion of a number such as 33: Easily done.
• "33abc": Results are in “Not a number, which will render NAN”
• True becomes 1, then the vice verse the values assigned as “True” or “False”
• Please do not WAR because it creates too many issues.

Short Summary Javascript

• Javascript data conversion is a critical thing to do well.
• Var are block and scope.

Operations in Javascript and Conversions

• Javascript operation of 2+2 results in 4, also same with - * /

• Javascript uses ** to calculate for ‘to the power' expression

• Modular operator is used in Remainder, important skill in cryptography.

• Javascript String can be concatenated together using “+” in their variable names. Example in notes below.

  str1 = "Hello"
  str2 = “Hitesh”
  console.log (str1 + str2). //Output = Hello Hitesh
  

More details about Operations in Javascript

• “1” + 2 becomes 12, this is a very common string javascript functionality
• 1 + “2” also becomes 12
• “1 + 2” also gives “12”
• 1 + 2 + 2 renders 122 after the quotes are closed.
• • True = 1
• Double + operation error "not expected."
• Empty parenthesis returns 0
• Value 1 == 2 & 2=3 are not well used or followed, and should be avoided. A better way is to use Parenthesis.
• Game counter ++ expression will print +1 value higher immediately. Important to read and reference increment Operators with - JS and MDN documentation at that reference, check Examples that includes +x and x++ small. Code here just to check JS mdn.

Mdn Documentation to check

• All of the operators here which is important to check precedence with Javascript MDN:
• It starts with: Priority and Association of Expressions, Operators: MDN is the link to study MDN documents.

Comparison Operators in JS

• Comparison operators in Javascript that result in boolean values include: <, >, <=, >=, == (!=), !=.
• Can compare 2 numbers: "2 > 1" results in boolean values.
• Can compare Strings and has the same result like Numbers.

Javascript Problems with Comparision

• If you dont’ use the same Data Type, you could encounter non predicted boolean Results: "2 > 1 “
• Type conversions should be fixed. If this rule exists, there is no need for libraries like Typescript.
• To avoid comparison issues between Data Types, always use only one data Type to avoid “issues” that come with Javascript, even when it provides predicted outcomes as a Type.

Special Notes - Datatypes

• Compare in code with Nulls and Undefined: there are special cases here which have different rules and can result in errors in Javascript.

Null

• Javascript automatically converts null as “0”, you can prevent the value by just setting it to false but also make sure the appropriate error handling to avoid mixing Null with 0.

Undefined

• If comparing with Undefined, all Javascript is always false as by the rules of JS.
• Equal, greater than/ less than / equals are treated differently by the Engine compared to Comparision.

Tips for Coding

• These types are generally used for questions and not practical / use-able purposes. Always look at "Clean Code." - Javascript checks with Triple Equal - if the type is actually same and compares with a Triple equals to have very explicit data type and the code wont run and avoids these edge cases.

Last Thoughts

• General takeaways: please, in terms of Javascript and general points to avoid with the above mentioned scenarios that can go wrong as highlighted for these cases/scenarios.

Data Types in Summary

• Data Types for the assignment from that Javascript has from the ecmascript with MDN are all mentioned in the notes!

Javascript Memory

• This section contains how to implement memory in javascript. Memory or thread of javascript are hard to grasp concepts
• Previously, early languages such as C required a programmer to know where and how memory runs
• However, mordern javascript allows automatic memory and removes control of the old days.
• Two types of javascripts memory in this memory lecture

Data Types Part 2

• Primitives
• Non Primitive & Reference
• Difference is what it stores & how its managed.

Memory Stack

• 2 Types
• Stack & Heap memory
• Primitives are in the Stack Memory
• Non Primitives in Heap
• Heap: gives Reference to the Value in memory.

Tips on Javascript

• Avoid making assumptions and check memory if can to see. Can be a test and investigation effort. Do not rely on testing all the time and ensure proper checks.
• If Memory can be managed - look into code.
• Stack copies over values from old.
• Heaps take reference of the same values again and not another value like stacks.

Varities of Loops: Memory Testing

• In Chrome's console of memory can see Javascript's reference to data in heap and stack:

To test create a simple code:

const user =….
UserTwo = user

• Now change any variable of first & it will affect the other. Since object is copied its a shared reference, value - and it is not a reference of copy
• Test it yourself and check with a friend - and do your own tests with all sorts of test

Notes

• Primitives -> get copy
• Heaps ->reference

Javascript and Conversions

• In Javascript, be careful of scope issues using VAR. Use CONST & LET. In short please don’t rely on javascript comparisons. Look at this more!

JS in Code

Basic Example:

NegativeValue = -isValue is the basic example.

• No code execution. Run test in MDN and run them and get details tested in Mdn documentation:
• Code will be added here. Get MDN - Prefix, Postfix Javascript and also read the Code:
• All of it is covered !

Conversions into Javascript - Study Notes

• Please look into the Ecma for JS and specifications for specifications

Control Flow in Javascript

• Now, we'll explore several ways to control code execution, including if-else statements, for- of loops, and the switch data flow control mechanism. This discussion explores these core concepts more than other sections in this MDN Javascript tutorial.

Conditional Statement: Ifs in JS

• If the statement with a variable comparison using < == is common. Most of what was previously covered will cover this but still basic with the Javascript.

Note

Javascript Equal and Type of are separate things.

• Triple equals check type and code with values.
• Clean code & avoid being confused with things that happen with Code.

Loop to Learn Javascript with Tests

• Here are some sample things to learn to play with: Check one thing - use that as a check - please copy that link from somewhere: Javascript + MDN Javascript. 0

Short Codes in Javascript

• Then start playing with Short code - but in test files and not real code! So make them in separate ways and know these ways and their code and run them at test and play around with them and check all this in MDN. Do this work. Then check everything. Run and play around in Javascript. Make this simple

In Brief

Learn basics on JS in code to find their bugs. The same code of Javascript. It has become simple to see!

Details

MDN Increment Operator - just check that page is good

Switch

• Switch statement controls multi - direction, multiple statements or codes/codes based on the same criteria

Notes

• Link to study
• Get more at: Code !

Dates

• Javascript date is a pain point with Javascript! How and When to run it. And how we run all of it.

To Date time Conversion

• All Javascript files are done and push all of it. A ton of content to test all of that!

Date Testing

• So let's study all of it! The data types from MDN Javascript documentation. The TC39 link with the Date documentation in that page!

Basic Dates in Javascript

• Date with javascript = January 1 / 1970 - there are millions of miliseconds that it runs.
• So dates have to declare all of these dates, here too!

Date JS

• https://developer.mozilla.org/en-US/docs/Web/Javascript/Reference/Glob al_Objects/Date
• TC39. Es / https://tc39.es
• TC39 to fix with Temporal as the next plan, fix!
• https://github.com/tc39/proposal-temporal- get more dates now as the temporal has an effect of the data in MDN - now it seems like we all good from what the Temporal MDN has done!
• All the code works!

Date Methods with Javascript ES

Basic

• Run the “now" method! Run many and see all of the different outputs - please code here that we have coded

Note

Date JS is an "object.“ Type of date JS prints = object with TypeOf!

MDN Date - Check and See!

https://developer.mozilla.org/en-US/docs/Web/Javascript/Reference/Glob al_Objects/Date

You have to look at MDN code.

TimeStamps

• What Is that code ? - check MNN documentation if need by. It's easy. Then read more in the Javascript with MDN

How to print code nicely and present it better !

• If you want the code to present better. Check out the Javascript in MDN for that! 🤣

Code push : dates

• Add and commit and push.
• Enjoy the video ! Next all do together! More! So yeah, that is all

While Loop

• Very similar to an "if-else" statement, but loops through code as long as the condition is true.
• Only checks a condition and executes code repeatedly.
• Requires initialization, condition check, and increment/decrement of a variable.

Structure

• Initialize a variable (e.g., index = 0).
• Set a condition for the loop to continue (e.g., index <= 10).
• Execute code within the loop.
• Increment or decrement the variable to eventually terminate the loop.
• Failure to increment or decrement results in an infinite loop.

Array Iteration with While Loop

• Initialize an index variable to 0.
• Set the condition to check the index against the array's length.
• Access array elements using the index.
• Increment the index in each iteration.

Do-While Loop

• Condition is checked at the end of the loop after the "do" block has been executed.
• Guarantees that the code block is executed at least once.
• Structure of Do-While loop differs as work is done before condition is checked.
• Work is carried out before condition is verified
• Uncommon to use, prefer checking conditions first in regular flows though exceptions happen

Execution

• Code inside the "do" block is executed first.
• Condition in the "while" statement is checked after execution.
• Loop continues if the condition is true.

Special Case

• Work gets done first, then condition is checked
• If the initial value doesn't satisfy the condition, the loop still executes once.
• One-time use cases sometimes need do-while

Specialized Loops for Arrays

• Loops are specialized for looping through arrays since it is a common function.
• Databases return values are in array format.
• APIs are usually in array format.
• Specialized loops were built in arrays.
• for...in loop, forEach loop, and for...of loop.
• Syntax differences, use whichever loop you like.
• Practical examples make concepts easy to understand, like Three.js.
• The material to be covered includes for...of loops, higher-order functions, array-specific loops, and JavaScript's powerful arrays and objects.
• Common scenarios involve arrays containing various objects, and the need to extract values from these objects.

For...of Loop

• A for...of loop iterates over iterable objects like arrays, strings, and potentially objects (though with caveats).
• The syntax is for (const iterator of object) { // code }.
• iterator is a variable declared with const that represents the element being processed in each iteration.
• object refers to the iterable object (array, string, etc.) over which the loop is running.
• It is not necessary to manually specify the array size or handle increment/decrement logic.
• The loop works regardless of what is in array, be it string, int, float, etc
• Can be used with strings to iterate over each character.
• continue and break keywords can be used to control flow within the loop.

Maps and For...of Loop

• Maps are a datatype in in JS that are kind of similar to arrays, but are very unique
• Maps hold key-value pairs, similar to objects.
• Maps remember the original insertion order of the keys
• Maps enforce uniqueness of keys (no duplicates).
• .set() is used to populate a map
• .get() is used to retrieve a value
• When iterating over a map with for...of, each element is an array containing the key-value pair.
• Array destructuring can be used within the loop to extract the key and value separately: for (const [key, value] of map) { // code }.

For..in Loop

• The for...in loop can be used with objects
• Syntax is for (const key in object) { //code }
• For...in loops iterate over the keys of an object.
• To access the value associated with each key, use bracket notation: object[key].
• Can be used on arrays, but it will iterate over the indices (keys) rather than the values directly.

Important Comparison point

• For..of will return the values of iterables where as For..in will need the respective objects to return the value itself.

ForEach Loop

• A forEach loop is an array method
• A forEach loop offers a simple mechanism for iterating over array elements
• Syntax : array.forEach(function(currentValue, index, arr), thisValue)
• currentValue is the value of the current element in the array
• index is the index of the current element in the array
• arr is the array object that the current element belongs to.
• thisValue is optional, value to use as this when executing callback

Higher-Order Functions

• Definition: A function that either takes a function as an argument or returns a function.
• The forEach loop is a higher-order function because it accepts a callback function as an argument.
• Callbacks can be defined inline (anonymous functions) or as separate, named functions.

Array iteration considerations

• ForEach, Filter and map are common methods to traverse arrays

CallBack Definitions recap

• A callback function is a function passed as an argument to another function, to be executed later.
• If the callback is defined inline as an anonymous function, its name is omitted.
• Arrow functions provide a concise syntax for defining callbacks.
• The forEach method automatically passes the current element.

ForEach Function parameters

• The callback function passed to forEach can accept up to three arguments: the current item being processed, its index, and the array itself.

Common Data Structures with Objects and Arrays

• A common scenario is the need to iterate over an array of objects and extract specific properties from each object
• The forEach loop allows to access each element of the array and subsequently its properties

Returning Values with ForEach

• ForEach does not return anything
• To get value from filter, you need to manually set the value for each iteration

Filter Method

• The filter method returns a new array containing all elements that pass a given test (provided as a callback function).
• If the code block within the callback function is enclosed in curly braces, you must use the return keyword to explicitly return the value that determines whether the element should be included in the new array.
• Without a return statement, the filter method will not include any elements in the new array.
• Filter takes a callback function
• You can perform logical operations to verify parameters and return a response
• Can define a parameter to get all objects within a set constraint
• Example given to publish post from a set timeframe

Arrow function

• To return the values, you should avoid using code block
• If returning a value from method, return statement must be manually used

Map Method

• The map method creates a new array by applying a function to each element of an existing array.
• Similar to filter, you can use explicit/implicit type returns from methods
• All rules for returns apply for that
• Can return new values with the transformed values

Chaining

• Is running multiple functions across a single array object
• The result of the map methods is always an array
• Chaining can be performed by attaching method to functions
• Chaining will not work if result is any other value besides array

Reduce Method

• Useful for Shopping Carts / Price aggregations

• Executes a user-supplied “reducer” callback function on each element of the array, in order, passing in the return value from the calculation on the preceding element.

• The final result of running the reducer across all elements of the array is a single value.

• Takes in a call back

• Has a default value called accumulator

• Always used with arrow functions

• With each iteration, the accumulator collects the value of the previous result, to be used in current process

• Useful when combining value of various array and objects

• Example - add price for all items in shopping cart

• Set a condition for the loop to continue (e.g., index