Ivo Wetzel covers some of the quirks of the JavaScript language. Some of these cause subtle bugs, some overturn conventional wisdom. It covers toString on numbers. Covers the advanced JavaScript features such as prototypal inheritance, this, closures, anonymous wrappers, type-casting, automatic semicolon insertion and hoisting of function and variable declarations.
Based on Simon Willison's original 2005 eTech talk, Simon expands this into a full article covering the expressive functionality of JavaScript. He covers the basics of JavaScript: literals, variables, functions, scope, control flow, objects, classes, inner functions and closures. Everything a developer needs to know before diving into more advanced JavaScript.
Ben Cherry, web developer at Twitter, takes us step by step through the Module Pattern. He introduces the standard features of Anonymous Closures and avoiding global scope, and covers advanced concepts such as augmentation, cloning, inheritance, private state and sub-modules.
A simplified explanation of closures by Morris Johns: A closure is the local variables for a function - kept alive after the function has returned.
A stackoverflow community article explaining closures in plain simple English does a great job. Succinctly: a closure is created when inner function that gets returned. The inner function can still see the variables and methods defined in the outer function.
A clever hands-on interactive mini-course by Nathan Whitehead that guides you through bite-sized chunks from variables, to functions, to return values, to functions as first-class objects and right into closures and finally continuations. The hands-on exercises are JS Linted and unit-tested which gives you ample space to try out your new-found knowledge.
Douglas Crockford explains the new strict mode introduced in the 5th edition of ECMAScript. It is an opt-in mode that repairs or removes some of the language's most problematic features such as: function scoping, implied global variables and global leakage, read-only variable failures, octal defaults and function arguments.