The scope of variables in JavaScript is determined by the keywords
used to declare them. `var` variables have function-level scope,
meaning they are visible throughout the entire function in which
they are declared, or even globally if not within a function,
potentially leading to unintended variable collisions. `let` and
`const` variables, on the other hand, have block-level scope,
meaning they are limited to the block (enclosed by curly braces) in
which they are defined. This prevents variable leakage and allows
for more predictable and safer variable management. Additionally,
`const` is used for constants, which cannot be reassigned after
declaration, ensuring that the value remains fixed within its block
scope. These distinctions in scope and behavior make `let` and
`const` generally preferred over `var` for modern JavaScript
development.
null and undefined are both JavaScript values used to represent the
absence of a meaningful value, but they are used in different
contexts. `null` is typically assigned by a programmer to indicate
the intentional absence of an object or value, often used when you
want to explicitly set a variable or property to "nothing." On the
other hand, `undefined` usually indicates that a variable or
property has been declared but hasn't been assigned any value yet,
or it can be a result when trying to access non-existent object
properties or function parameters that haven't been provided. Use
cases for `null` include explicit value absence, while `undefined`
is more about the absence of assignment or expected values in
various contexts.
REST, which stands for Representational State Transfer, is a
software architectural style that defines a set of constraints for
designing networked applications. RESTful APIs (Application
Programming Interfaces) are a type of web service that adhere to
these constraints. In a REST API, resources are represented as
unique URLs, and interactions with these resources are performed
using standard HTTP methods such as GET (retrieve data), POST
(create data), PUT (update data), and DELETE (remove data). The key
principles of REST include statelessness, meaning each request from
a client to a server must contain all the information needed to
understand and process the request; a uniform interface for
consistency and simplicity; and a client-server architecture that
separates the user interface concerns from the data storage and
retrieval concerns. REST APIs are widely used for building scalable
and interoperable web services, making them a fundamental part of
modern web development and integration.