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.