ECMAScript

ECMAScript can be defined as the specification for defining a general purpose language. It provides rules, guidelines and details that scripting languages must observe to be ECMAScript compliant. JavaScript is the only scripting language that it regulates.

ECMAScript 5

The following keywords provide Block Scope Variables (and constants).

let

Before ECMAS2015 Variables declared inside a function (locally) have what is described as Function Scope .Local variables can be accessed ONLY inside the function.

Global Scope

Block scope

const

ECMAScript 6