The document discusses various JavaScript concepts including ECMAScript, the difference between ES5 and ES6, web crawlers, DOM manipulation, OOPs in JavaScript, data structures like Set and Map, symbols, JavaScript engines, and recursion. ECMAScript is the standardized language specification while JavaScript is the programming language. Key differences between ES5 and ES6 include new features added in ES6 like modules and default parameters. Web crawlers systematically browse pages on the web to index content. JavaScript allows OOPs concepts like abstraction, encapsulation, inheritance and more through its prototype-based approach. Common JavaScript engines include V8, SpiderMonkey and Chakra.

1. Tutorial - 8
• ECMAScript
• ES-6 vs ES-5
• ES-6 (modules & default parameters)
• Type conversion
• JS window object
• Web page crawler
• Element selector in JS
• DOM manipulation via API calls
• OOPs in JS
• Set, Weakset, Map & Symbol
• JS-Engine
• Recursion in JS
• Constructors in JS
• JS- decorators
• JS array with -ve index
(question)

2. ECMAScript
• ECMAScript is the general-purpose programming language which
is standardized by ECMA International following ECMA-262
document
• ECMAScript is different from JavaScript:
⚬ https://stackoverflow.com/questions/912479/what-is-the-
difference-between-javascript-and-ecmascript
• JavaScript is older then ECMAScript
• ECMAScript is the standard of language and JS is the language
• https://stackoverflow.com/questions/912479/what-is-the-difference-
between-javascript-and-ecmascript
• https://www.freecodecamp.org/news/whats-the-difference-between-
javascript-and-ecmascript-cba48c73a2b5/

3. ES-5 vs ES-6
• https://engineering.carsguide.com.au/es5-vs-es6-syntax-6c8350fa6998
• https://www.javatpoint.com/es5-vs-es6
• https://morioh.com/p/0236f0adaa4a (POINT-4)
• https://frontend.turing.edu/lessons/module-2/es5-vs-es6.html

4. web page crawler
• A Web crawler, sometimes called a spider or spiderbot
and often shortened to crawler, is an Internet bot that
systematically browses the World Wide Web, typically
operated by search engines for the purpose of Web
indexing (web spidering)
• When crawlers find a webpage, our systems render the
content of the page, just as a browser does. We take note
of key signals

5. Web crawler working model

6. Minor our own cralwer

7. Element selector

8. https://javascript.info/searching-elements-dom

9. OOPs in JavaSctipt
• OOPs or Object Oriented Programming is practice of a concept to have your code in
the form of objects which have either attributes or functions
• Major properties in JS are :
⚬ Abstraction,
⚬ Encapsulation,
⚬ Polymorphism
⚬ Inheritance
• Is JavaScript OOPs language:
⚬ Yes it is but its different from other OOPs language
⚬ It is prototype based object oriented language, which means it doesn’t have
classes rather it define behaviors using constructor function and then reuse
it using the prototype.
• https://www.geeksforgeeks.org/introduction-object-oriented-programming-javascript/

10. Set, WeakSet, Map & Symbol
• Set is elements with unique set of values i.e. there will be no repetition of
any value

11. Examples

12. Create unique elements in an array
• Note:
⚬ Only iterrable data-types like arrays are only allowed in Set
⚬ Hence objects cant be added to Set

13. WeakSet
• WeakSet let you add only object, Array of object
• It doesnt allow adding of premitive types & array of primitive types
• WeakSet allows Iterable data types but weakset itself is not an iterable henceit
cant be run by any loop
1 & 3

14. Map
• Map gives us the flexibility to accomplish the storage of any value in with the
clear information of key and value
• When we have an object why we need the Map then:
• Reason is:
⚬ Because if an object is having a key as an object then it can accept that
key only with one value depth whereas thats not so with Map
output when an object is considered instead
Map
Note: here only line 9 is present in
O/P

15. Note: here both assignment of value i.e. line 10 & 11 are present

16. Symbols
• https://developer.mozilla.org/en-
US/docs/Web/JavaScript/Reference/Global_Objects/Symbol
• https://flaviocopes.com/javascript-symbols/
• https://javascript.info/symbol
• Symbol doesn't use new keyword for its declaration
• Symbol is inerrable
• Symbol is also a primitive data-type in JS
• It’s a very peculiar data type. Once you create a symbol, its value is kept
private and for internal use.
• object property keys may be either of string type, or of symbol type. Not
numbers, not booleans, only strings or symbols, these two types

17. JS- Engine

18. JavaScript at runtime
environment

19. • A JavaScript engine is a computer program that executes
JavaScript code. The first JavaScript engines were mere
interpreters, but all relevant modern engines use just-in-time
compilation for improved performance.
• Some famous JS engines are:
⚬ Google , Chrome, Node, Deno - V8
⚬ Mozila Firfox - SpiderMonkey
⚬ Microsoft Edge- Chakra
• Oldest one is Spider money by Brenden Eich (Inventer of JS)
when he was with Netscape
• JS engine is not a hardware but a code snippet only

20. • Steps followed by JS engine are:
⚬ Step-1 (Parsing)
￭ Here our code is get converted to AST i.e. Abstract Syntax
Tree, which is the passed into the interpreter & after applying
algorithms like Mark & Sweep to remove unused code, we
then pass that code snippet to 2nd Step
⚬ Step-2 (Compilation)
￭ Here compilation of code takes place which is then passed for
last sept
⚬ Step-3 (Execution)
￭ Here in the last step Execution takes place which is performed
on completely optimized code