5 Core JavaScript Concepts Intermediate Developers Should Deeply Understand

A technical guide published on DEV Community outlines five foundational JavaScript concepts that often trip up intermediate developers despite their practical experience. The topics covered include execution contexts and hoisting, where variables declared with var are initialized to undefined while let and const enter a Temporal Dead Zone before their declaration. The guide also breaks down the four primary rules governing the this keyword, noting that arrow functions lexically inherit this rather than defining their own. Closures are explained as a mechanism for retaining access to outer function variables even after execution ends, historically used to simulate private state. The article aims to help developers move beyond framework familiarity and build a stronger grasp of how JavaScript behaves under the hood.