Lexical Scoping (or Static Scoping) Vs Dynamic Scoping

Static (or lexical) scoping and dynamic scoping are two different ways that programming languages determine the scope of a variable. JavaScript uses lexical scoping.

Lexical Scoping (Static Scoping):

  • In lexical scoping, the scope of a variable is determined at the time of the code’s creation (i.e., during the lexical analysis or parsing phase).
  • The scope of a variable is based on its location in the source code.
  • When a function is defined, it “captures” the scope in which it is defined, and it has access to the variables in that scope, as well as any outer scopes.
  • This is the most common type of scoping and is used in languages like JavaScript.

Example in JavaScript:

function outer() {
  let x = 10;

  function inner() {
    console.log(x); // inner has access to the variable x in the outer scope
  }

  inner();
}

outer();

Dynamic Scoping:

  • In dynamic scoping, the scope of a variable is determined at runtime based on the flow of the program.
  • The scope is determined by the current execution context or the function call stack.
  • Languages like JavaScript use lexical scoping rather than dynamic scoping.

Example (hypothetical) dynamic scoping behavior:

function outer() {
  let x = 10;
  inner();
}

function inner() {
  console.log(x); // If using dynamic scoping, this might look for x in the calling context (outer), not the defining context (inner)
}

outer();

In summary, JavaScript employs lexical scoping, where the scope of a variable is determined by its location in the source code. This is contrasted with dynamic scoping, where the scope is determined at runtime based on the program’s execution context.


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