Mastering JavaScript

ECMAScript 6
Using standalone brackets {} may seem unusual in JavaScript, but this convention is
fairly common to create a block scope in many languages. The block scope kicks in
other constructs such as if { } or for (){ } as well.
When you use a block scope in this way, it is generally preferred to put the variable
declaration on top of the block. One difference between variables declared using
var and let is that variables declared with var are attached to the entire function
scope, while variables declared using let are attached to the block scope and they
are not initialized until they appear in the block. Hence, you cannot access a variable
declared with let earlier than its declaration, whereas with variables declared using
var, the ordering doesn't matter:
function fooey() {
console.log(foo); // ReferenceError
let foo = 5000;
}
One specific use of let is in for loops. When we use a variable declared using
var in a for loop, it is created in the global or parent scope. We can create a blockscoped
variable in the for loop scope by declaring a variable using let. Consider the
following example:
for (let i = 0; i