Scope determines the accessibility (visibility) of variables. JavaScript variables have 3 types of scope: Block scope; Function scope; Global scope

Global Scope. Variables declared with the var always have Global Scope. Variables declared with the var keyword can NOT have block scope:

Hoisting is JavaScript's default behavior of moving all declarations to the top of the current scope (to the top of the current script or the current function). The let and const Keywords Variables …

All JavaScript variables must be identified with unique names. These unique names are called identifiers . Identifiers can be short names (like x and y) or more descriptive names (age, sum, …

Block Scope. Declaring a variable with const is similar to let when it comes to Block Scope. The x declared in the block, in this example, is not the same as the x declared outside the block:

You can use the JavaScript typeof operator to find the type of a JavaScript variable. The typeof operator returns the type of a variable or an expression: Example

JavaScript let. The let keyword allows you to declare a variable with block scope.

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A closure is a function that has access to the parent scope, after the parent function has closed. Closures has historically been used to: Create private variables; Preserve state between …

For security reasons, eval() is not allowed to create variables in the scope from which it was called. In strict mode, a variable can not be used before it is declared: "use strict";