Salesforce JavaScript Developer Practice Exam 2025 – Comprehensive Test Prep

A closure in JavaScript is defined as a function that retains access to its lexical scope, even when the function is executed outside that scope. This concept is fundamental in JavaScript due to its function scoping and the ability for inner functions to remember the environment in which they were created.

When a function is defined within another function, the inner function forms a closure, capturing the variables that are within its lexical scope. This means that the inner function can access those variables even after the outer function has finished executing. This capability allows for the creation of private variables, encapsulated behavior, and helps maintain state in a controlled manner.

For instance, consider a function that returns another function, which then references variables from its parent function. Despite the parent function having completed execution, the inner function still has access to those variables. This feature is widely used in JavaScript for various purposes such as creating factories, event handlers, and modules.

This understanding of closures is essential for effective JavaScript programming, particularly in relation to asynchronous programming, callbacks, and event handling, where functions may be executed outside their original scope.