🌟 Scope

Explanation: Scope is the accessibility of variables, functions, and objects in a specific part of the runtime code.
Scope: The biggest use of scope isSegregation variableVariables with the same name in different scopes do not conflict.
Features: Scopes are layered, with inner scopes having access to variables in outer scopes, but not vice versa.
Before ES6, JavaScript had no block-level scope, only global scope and function scope. With the advent of ES6, we have ‘block-level scope’, which can be embodied by the addition of the let and const commands.

Explanation:Objects that can be accessed anywhere in the code have global scope.
Common:
1) Outermost functions and variables defined outside the outermost function have global scope
2) All variables that are not directly assigned are automatically declared to have global scope
3) All properties of the Window object have global scope

Explanation:A function scope is a variable declared inside a functionIn contrast to global scopes, local scopes are generally accessible only within fixed code snippets, most commonly within functions.

Block-level scopes can be declared with the new let and const commands. Variables declared cannot be accessed outside the scope of the specified block.
Create:
1) Inside a function
2) Inside a code block (enclosed by a pair of curly braces)
Features:
1) Declaration variables are not promoted to the top of the code block, and let/const declarations are not promoted to the top of the current code block
2) Repeat statements are prohibited
3) Bound block scope in loop

🌟 scope chain

Variables not defined in the current scope