Scope

The scope is the current context of execution in which values and expressions are “visible” or can be referenced. If a variable or expression is not in the current scope, it will not be available for use. Scopes can also be layered in a hierarchy, so that child scopes have access to parent scopes, but not vice versa.

Global scope: The default scope for all code running in script mode. Module scope: The scope for code running in module mode. Function scope: The scope created with a function.

In addition, identifiers declared with certain syntaxes, including let, const, class, or (in strict mode) function, can belong to an additional scope: