export default function taskBlock(trueOrFalse) {

  var task = false;

  var task2 = true;

​

  if (trueOrFalse) {

    var task = true;

    var task2 = false;

  }

​

  return [task, task2];

}

Within the function, we first declare the name 

variable with the var keyword. This means that 

the variable gets hoisted (memory space is set 

up during the creation phase) with the default 

value of undefined, until we actually get to the 

line where we define the variable. We haven't defined

the variable yet on the line where we try to log the 

name variable, so it still holds the value of undefined.

​

Variables with the let keyword (and const) are hoisted,

but unlike var, don't get initialized. They are not

accessible before the line we declare (initialize) 

them. This is called the "temporal dead zone". When we 

try to access the variables before they are declared, 

JavaScript throws a ReferenceError.

​

function sayHi() {

  console.log(name);

  console.log(age);

  var name = 'Lydia';

  let age = 21;

}

​

sayHi();

​

​

​

hoistedVariable = 3;

console.log(hoistedVariable); // outputs 3 even when the variable is declared after it is initialized   

var hoistedVariable;

/*

Hoisting in JavaScript is a behavior in which a function 

or a variable can be used before declaration

*/

​

// using test before declaring

console.log(test);   // undefined

var test;

// program to display value

a = 5;

console.log(a);

var a; // 5

// hoisting is as if your `function fun() {}` was located here. 

​

fun(); // works. 

​

function fun() {}

var defaultname = "John";

var name = "rayn";

​

function doit() {

  if(!name){

        var name = defaultname;

  }

  return name;

}

​

var ourname = doit();

console.log(ourname); //John

// because name inside function will have more priority over outside name variable. 

// And, this inside name variable will be declared in memory as undefined due to hoisting.

​

x = 5; // Assign 5 to x

​

elem = document.getElementById("demo"); // Find an element

elem.innerHTML = x;                     // Display x in the element

​

var x; // Declare x

// accessing class

const p = new Person(); // ReferenceError

​

// defining class

class Person {

  constructor(name) {

    this.name = name;

  }

}

var a = 10;

{

    var a = -10;

}

let b = a;

{

    let b = -20;

}

​

console.log(b)