Scope
The current context of execution. The context in which values and expressions are "visible" or can be referenced. If a variable or other expression is not "in the current scope," then it is unavailable for use. Scopes can also be layered in a hierarchy, so that child scopes have access to parent scopes, but not vice versa.
A function serves as a closure in JavaScript, and thus creates a scope, so that (for example) a variable defined exclusively within the function cannot be accessed from outside the function or within other functions. For instance, the following is invalid:
function exampleFunction() {
var x = "declared inside function"; // x can only be used in exampleFunction
console.log("Inside function");
console.log(x);
}
console.log(x); // Causes error
However, the following code is valid due to the variable being declared outside the function, making it global:
var x = "declared outside function";
exampleFunction();
function exampleFunction() {
console.log("Inside function");
console.log(x);
}
console.log("Outside function");
console.log(x);
See also
- Scope (computer science) on Wikipedia