• JavaScript has function-based scope. Each function you declare creates a bubble for itself. All variables and functions created inside a function cannot be accessed outside of it.
• Variable collision needs to be avoided as a scope is accessible to all the nested scopes.
• Libraries loaded in the program can easily collide with each other if they do not properly hide their internal private functions and variables. Libraries typically create a single variable that is sufficiently unique in the global scope and then add properties on that object like

var myLibrary {
	greet: "Have a nice time",
	doSomething(): function() { .. }
	doSomethingElse(): function { .. }
}

• Another option is to use modern package managers to do the module management which can help us do explicit imports into the scope.
• JS also offers a way to create a function that doesn't pollute the current scope and has need not to be called separately. This tool is called function expression.

var a = 2;

// We start the function with `(` treated the function as function declaration
(function foo() { 
	var a = 3;
	console.log(a); //3
})(); // This is added to execute the function on the spot (IIFE)

foo(); // foo is not defined

• Anonymous function expressions are also commonly seen in JS. These are function expressions with no name.

setTimeout( function() {
	console.log("I waited 1 second!");
}, 1000);

• Immediately Invoked function expressions (IIFE) are having a () in the end to execute it. There are two ways: ( function iife() { .. })() ****or ****( function iife() { .. }()).
• We can pass argument to IIFE like

var a = 2;

(function IIFE(global) {
	var a = 3;
	console.log(a); // 3
	console.log( global.a ); // 2
})( window );

console.log( a ); // 2

• Block scope can be observed in JS at various places like with , try/catch , let and const.
• The frowned upon way of doing things using with has a block scope

var obj = {
	a: 1,
	b: 2,
	c: 3
};

// using with()
with(obj) {
	a = 2;
	b = 3;
	c = 4;
}

a; // not defined

• try/catch also has a block scope which was added in ES3

try {
	undefined();  // illegal operation to force error
} catch (err) {
	console.log(err);  // works!
}

err; // not defined

• let was added in ES6 and it is the most common way to create block as scope. let isn't hoisted (we will understand more about this in next chapter).

{
	let hello = "world";
}

hello; // not defined

• let also helps do better garbage collection