LET and CONST

Let & Const

In ES6 these replace the Var keyword. This is because they have an added feature block scoping.

A block is defined by the {} in JavaScript.

//This is block 1
{
//This is block 2
}
{
//This is block 3
	{
        //this is block 4
    }
}

You will see that for blocks 2 & 3 they are on the same level. they can have the same variable via let.

But, if you use a variable in, say block 3, the JS engine will look in block 3 & block 1 (its parents) for the variable before saying undefined.

This means you should use LET in place of var as much as possible.

Const

const is also block scoped. But its Binding is immutable! not the actual value!

const name = "Dan";
name = "Daniel"; //this will throw an error AS THE BINDING is being changed. 

const person = { name: "Dan", age : 123}
person.name = "Daniel" 
//This is fine as the binding between person and the memory is maintined!