You Don't Know JS: Scope and Closures2014

Closures have served as the boundary between developers who know how to use JavaScript to manipulate objects and developers who know how to use JavaScript to create libraries. The JavaScript renaissance has thrived in large part because closures give developers the power to manage JavaScript scope issues, but figuring out closures has remained difficult. This compact guide explores JavaScript scope in greater depth than previous treatments, defining the problems that closures solve, demonstrating why they work, and showing developers how to make closures a reliable standard part of their development toolkit.