What is hoisting?

The hoisting mechanism represents the behavior of the JavaScript interpreter in which variable and function declarations are moved to the top of their scope before code execution begins. It is important to understand that lines of code are not physically moved in the file, but memory for them is allocated in advance during the compilation phase. At the same time, the method of hoisting directly depends on the keyword used in the declaration. Variables created with var are hoisted to the top of the functional scope and automatically initialized with the undefined value, which is why they can be accessed before the declaration line, resulting in an undefined outcome rather than an error.

With the advent of let and const, the behavior changed to increase code reliability. Declarations via let and const are also hoisted, but they do not receive an initial value and are placed in the so-called temporal dead zone. Attempting to access such a variable before the line of its physical declaration in the code will result in a ReferenceError being thrown. As for functions, classical function declarations via function declaration are hoisted completely, including their body, which allows calling a function before it was written in the script text. At the same time, it is important to remember that only the declarations themselves are hoisted, not the value assignment operations for variables.