I created this repository because I often see frontend developer beginners focusing more on the framework/library rather than the fundamentals. I have created three folders with JS, TS, and CSS, covering various topics (including those most frequently asked in interviews) that can help build a solid foundation. Note: these are knowledge "bites", and I expect there to be a curiosity to investigate deeper at some point.

• Ajax vs JSONP
• Anonymous vs named vs arrow functions
• Callback hell, Promises and Async/Await
• Bundler vs transpiler
• Call vs apply vs bind methods
• Closure
• Coercion
• Const vs Object.freeze method
• Currying technique
• Dynamic import expression
• Event propagation, event bubbling and event capturing
• Event loop
• Generator functions
• Hoisting mechanism
• IIFE
• JS Engine
• Let vs const vs var
• Load vs DomContentLoaded event
• Map vs forEach loop
• Map vs weakmap vs set
• Module system
• Native and host objects
• New keyword
• Null vs undefined vs undeclared variables
• Optional chaining operator
• Polyfills and shims
• Prototypal inheritance
• Scope
• Script vs script async vs script defer tag
• Short circuiting evaluation
• Strict mode
• Symbol
• Template literals strings
• This keyword

• Abstract keyword
• Access modifiers
• Const assertion
• Declare keyword
• Enums
• Function overloading
• Generics
• Getters and setters methods
• Index signature
• Infer keyword
• Mixin
• Never type and never vs void type
• Non null assertion
• Override keyword
• Project references feature
• Structural typing
• Template literal types
• Unique symbol
• Unknown vs any type

• Block formatting context (rendering)
• Block vs inline vs inline-block properties
• Box model
• Document flow
• Flexbox vs grid
• How Css works
• Inheritance
• Pre processor
• Responsive design
• Specificity
• Stacking context
• Static vs relative vs absolute vs fixed position + translate()
• Variables
• Z-index property

• Accessibility
• Authentication strategies
• Content Security Policy CSP
• Client Side Rendering vs Server Side Rendering vs Static Site Generation
• Internet - HTTP - DNS - Domain Name - Web Hoisting - Browser
• OWASP Top 10
• Service Workers
• Local storage vs session storage vs cookies
• Web Sockets
• Web Workers

Remember to also put into practice what you learn: theory is good, but without practice, you won't be able to assimilate fundamental concepts. ESSENTIAL: maintain a curious mindset and avoid rushing, but above all, learn at a slow pace. Since these are dense topics, if you go too fast, you risk missing at least one-third of what was written above. So: go slowly + lots of practice. You've got this!

Fundamentals extend not only through JS, TS, and CSS but also through design patterns, data structures, and algorithms. Below, I will list a "must have" resources (both paid and free) that complement what has been written above. I strongly recommend the paid ones, as they are more comprehensive and also include interesting exercises that you can undertake: think of it as an investment in your future.

[paid]

Frontend Masters: Will Sentance - JS hard parts - v2

Frontend Masters: Kyle Simpson - Deep JS - v3

or

[free]

Kyle Simpson, You Dont Know JS - 1st edition

Kyle Simpson, You Dont Know JS - 2nd edition - STILL IN DRAFT

Eloquent JS

[paid]

Frontend Masters: Mike North - Typescript v4

Matt Pocock, Total Typescript

or

[free]

Learn Typescript

[paid]

Josh W Comeau, CSS for JS dev

[free]

Just the first modules about C, Data Structures and Algorithms: CS50 Harvard, Intro to Computer Science

[free]

Coursera: Software Design Architecture

Refactoring Guru, Design Patterns