Object Oriented

JavaScript has strong object-oriented programming capabilities, even though some debates have taken place due to the differences in object-oriented JavaScript compared to other languages.

Source: Introduction to Object-Oriented JavaScript
Anonymous Functions

Anonymous functions are functions that are dynamically declared at runtime. They’re called anonymous functions because they aren’t given a name in the same way as normal functions.

Source: JavaScript anonymous functions
Functions as First-class Objects

Functions in JavaScript are first class objects. This means that JavaScript functions are just a special type of object that can do all the things that regular objects can do.

Source: Functions are first class objects in JavaScript
Loose Typing

For many front-end developers, JavaScript was their first taste of a scripting and/or interpretive language. To these developers, the concept and implications of loosely typed variables may be second nature. However, the explosive growth in demand for modern web applications has resulted in a growing number of back-end developers that have had to dip their feet into the pool of client-side technologies. Many of these developers are coming from a background of strongly typed languages, such as C# or Java, and are unfamiliar with both the freedom and the potential pitfalls involved in working with loosely typed variables.

Source: Understanding Loose Typing in JavaScript
Scoping and Hoisting

Scoping: In JavaScript, functions are our de facto scope delimiters for declaring vars, which means that usual blocks from loops and conditionals (such as if, for, while, switch and try) DON'T delimit scope, unlike most other languages. Therefore, those blocks will share the same scope as the function which contains them. This way, it might be dangerous to declare vars inside blocks as it would seem the var belongs to that block only.

Hoisting: On runtime, all var and function declarations are moved to the beginning of each function (its scope) - this is known as Hoisting. Having said so, it is a good practice to declare all the vars altogether on the first line, in order to avoid false expectations with a var that got declared late but happened to hold a value before - this is a common problem for programmers coming from languages with block scope.

Source: JavaScript Scoping and Hoisting
Function Binding

Function binding is most probably the least of your concerns when beginning with JavaScript, but when you realize that you need a solution to the problem of how to keep the context of this within another function, then you might realize that what you actually need is Function.prototype.bind().

Source: Understanding JavaScript’s Function.prototype.bind
Closure Function

Closures are functions that refer to independent (free) variables. In other words, the function defined in the closure 'remembers' the environment in which it was created in. It is an important concept to understand as it can be useful during development, like emulating private methods. It can also help to learn how to avoid common mistakes, like creating closures in loops.

Source: MDN - Closures
Strict mode

ECMAScript 5's strict mode is a way to opt in to a restricted variant of JavaScript. Strict mode isn't just a subset: it intentionally has different semantics from normal code. Browsers not supporting strict mode will run strict mode code with different behavior from browsers that do, so don't rely on strict mode without feature-testing for support for the relevant aspects of strict mode. Strict mode code and non-strict mode code can coexist, so scripts can opt into strict mode incrementally.

Source: MDN - Strict mode
Immediately-Invoked Function Expression (IIFE)

An immediately-invoked function expression is a pattern which produces a lexical scope using JavaScript's function scoping. Immediately-invoked function expressions can be used to avoid variable hoisting from within blocks, protect against polluting the global environment and simultaneously allow public access to methods while retaining privacy for variables defined within the function.

This pattern has been referred to as a self-executing anonymous function, but @cowboy (Ben Alman) introduced the term IIFE as a more semantically accurate term for the pattern.

Source: Immediately-Invoked Function Expression (IIFE)