Javascript:

• "You Don't Know JS" A definitive resource on all the juicy bits of Javascript. I recommend reading it from start to finish. Highly recommended for all levels of webdev.
• "Eloquent Javascript" Another good long-form resource on the syntax of Javascript. Good for beginners.
• "Quora - What should I study to get into Hack Reacktor?" From the CEO (at the time) of Hack Reactor a definitive list of what you need to know to get into Hack Reactor (at the time). A good general study list for beginners considering trying to get into a Javascript bootcamp.
• "Understand Javascript Callback Functions and Use Them" My oft-recommended article to newbies having a hard time grasping how callback functions work in Javascript.
• "Understand Javascript Closures with Ease" Similar to above a great introduction to Javascript Closures.
• "Functional Programming in Javascript" A fantastic set of interactive exercises that utilize functional programming concepts. Basically has you stringing together map reduce etc functions. A GREAT resource for interview practice.
• "Javascript Exercises" A series of beginner exercises in Javascript. If you need tons of practice this is a good place to get it.
• "How Do Javascript Closures Work" A great Stackoverflow series of answers on Javascript closures. This is what sealed the deal for me in understanding.
• "Javascript Truthy Falsy" While the best way to learn in-depth how Javascript `==` and `===` works and their differences is to read "You Don't Know JS" this is a good quick reference.
• "Debugging Javascript" A quick intro to the critical tool of web development - the debugger console.
• "(Video) Javscript Closures Tutorial" For those that prefer videos this is the best one I know of that teaches about Javascript closures.
• "Ten Questions I've Been Asked... over Javascript Job Interviews" A great reddit post on what to expect in a web dev job interview. A good list of concepts to deep-dive in MDN.
• "Unit Test Views Best Practice" Unit testing views is tricky. If you aren't even sure where to start this Stackoverflow answer has some good tips.
• "Codewars" A coding challenge site.
• "Leetcode" A coding challenge site.
• "XMLHttpRequest" The MDN article on one of the core methods of AJAX aka one of the foundations of modern web development using single page apps. I highly recommend new web devs read this start to finish as well as read through to further links in the article.
• "Overview of Javascript ES6 Features" A good article for overviewing what was new for Javscript ES6/ES2015.
• "How Javascript Works: Inside the V8 Engine" Article and Hackernews discussion into the inner workings of the Chrome V8 engine. Very high-level but good to skim to get a better idea of how our core technology works.
• "All the Fundamental React JS Concepts Jammed into this... article" If you need to just quickly understand what React is this article is great.
• "Modern JS Cheatsheet" Quick examples of a bunch of JS concepts like the difference between let/var/const `this` references etc.
• "Node Best Practices"
• "Build an App with Vue.js: From Authentication to Calling an API" A fantastic article for those that just need to see what a whole app looks like in code. If you're unclear about what authentication looks like calling an API or how to implement all this in a web framework this is a great article to start with.
• "Exploring ES2018 and ES2019" A list and dive into what's coming in ES2018 and ES2019.
• "How to Javascript in 2018" A great overview of all the technologies web devs are using in 2018.
• "9 Promising Promise Tips" A great article for Promise usage in Javascript. Promises are often used incorrectly so it's important for newbies especially to read up on common pitfalls.
• "A Simple Guide to ES6 Promises" Another good article on Promise usage. Remember that any reasonable web dev interview will heavily cover Promises so it's important to know them inside and out.
• "Async-Await = Generators + Promises" A good article on the 4 key concepts introduced in ES2015/ES6.
• "Understand Javascript Promises by Building a Promise from Scratch" Building a Promise from scratch is a very important skill for those going into the more hardcore webdev interview situations i.e. at Google or similar. This is my favorite article on the subject though I have a couple others to help elucidate. My recommendation is for those hardcore interviews to know Promises well enough to implement them in vanilla Javascript.
• "Basic Javascript Promise Implementation Attempt" Another Promise implementation this time from StackOverflow.
• "A Tour of Javascript Timers on the Web" One of my favorite articles to recommend especially to newbies. You may learn more than just timers - it goes into the event loop. Recommended reading for interview prep.
• "You Don't Need jQuery" A list of methods that you can use instead of jQuery. Great for newbies to explore the vanilla Javascript API.
• "Lexical Scoping Paramters in Javascript" This is the Stackoverflow question that finally resulted in me understanding lexical scoping.
• "Demystifying JS Engines" Javascript engines aren't beyond your understanding. Highly recommended for people going into interviews, so you can talk the talk better than other interviewees.