What is scope and scope chain

What are scopes and scope chains

Scope
The area where the object can be called , Define a variable , Valid scope of variable

a(){
    
	let str = '1';
	let fun1 = function(){
    
	let str2 = '2';
	console.log(str,str2); // 1 2
	}
	console.log(str);// 1
	console.log(str2); // str2 is not defined
}

appeal str The scope of is a() Inside , str2 yes fun1() Inside

Scope chain
When calling a function or property , First look for in the current scope , If it cannot be found, look up the parent , Until the global scope is found , This Chain search The process of , It's the scope chain .