JavaScript – Blocks and IFFES

Let’s look at the new way to create IFFES!

Since variables declared with let and const are block-scoped which means these variables are defined inside of a block, and from the outside of the block they are not accessible.
This is exactly what we want,
–> Data Privacy

Before ES6, we use IFFES for that, it seems that in ES6, we have a much simpler way to achieve data privacy since all we have to do is to use a block.

A block is not restricted to if statement, for or while loop, we can also create a block simply like this

{   
  //your code
} 

And we just created a block !

{     
  const a = 1;     
  let b = 2;
} 

console.log(a + b); 
//Uncaught ReferenceError: a is not defined 

Since these values are not accessible from outside of the block, we got an error here. This reinforces the fact that they are block-scoped, not function-scoped.

So what we have here now is exactly like an IFFE, we created some data here that is not accessible from the outside.

It’s so much easier to write like this.

---

ES5 version to create variables that are inaccessible from outside

(function(){   
  var c = 3;   
  var b =2; 
})(); 
console.log(c+b); 

This was the old way.

---

What if

{     
  const a = 1;     
  let b = 2;     
  var c = 3; 
} 
console.log(c); 

The answer is

3 

This is because variable declarations with var keyword it does not matter whether they are inside of a block or not since

they are function-scoped. (instead of block-scoped)