Prehoisting

Prehoisting is a technique used in the field of software engineering, particularly in the context of JavaScript, to optimize the performance of code execution. It involves moving variable and function declarations to the top of their containing scope during the compilation phase, before the code is executed. This process is known as "hoisting."

In JavaScript, variable declarations using the var keyword are hoisted to the top of their function or global scope. However, only the declarations are hoisted, not the initializations. This means that a variable can be used before it is declared, but it will have an initial value of undefined until the declaration is encountered.

Function declarations are also hoisted to the top of their containing scope. This means that a function can be called before it is declared in the code. However, function expressions (where a function is assigned to a variable) are not hoisted in the same way. Only the variable declaration is hoisted, not the function assignment.

Prehoisting is an important concept to understand when working with JavaScript, as it can affect the behavior of code and lead to potential bugs if not properly managed. By understanding how hoisting works, developers can write more predictable and efficient code.