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A variable can be either of global or local scope. A global variable is a variable declared in the main body of the source code, outside all functions, while a local variable is one declared within the body of a function or a block. Modern versions allow nested lexical scope.
Non-local variables are the primary reason it is difficult to support nested, anonymous, higher-order and thereby first-class functions in a programming language. If the nested function or functions are (mutually) recursive, it becomes hard for the compiler to know exactly where on the call stack the non-local variable was allocated, as the frame pointer only points to the local variable of ...
The set of all global variables is known as the global environment or global state. In compiled languages , global variables are generally static variables , whose extent (lifetime) is the entire runtime of the program, though in interpreted languages (including command-line interpreters ), global variables are generally dynamically allocated ...
Local variables may have a lexical or dynamic scope, though lexical (static) scoping is far more common.In lexical scoping (or lexical scope; also called static scoping or static scope), if a variable name's scope is a certain block, then its scope is the program text of the block definition: within that block's text, the variable name exists, and is bound to the variable's value, but outside ...
The key to understanding design patterns such as IIFE is to realize that prior to ES6, JavaScript only featured function scope (thus lacking block scope), passing values by reference inside closures. [9] This is no longer the case, as the ES6 version of JavaScript implements block scoping using the new let and const keywords. [10]
The term closure is often used as a synonym for anonymous function, though strictly, an anonymous function is a function literal without a name, while a closure is an instance of a function, a value, whose non-local variables have been bound either to values or to storage locations (depending on the language; see the lexical environment section below).
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A namespace in computer science (sometimes also called a name scope) is an abstract container or environment created to hold a logical grouping of unique identifiers or symbols (i.e. names). An identifier defined in a namespace is associated only with that namespace.