JavaScript - What is hoisting of variable and function?

A variable defined with var and a function can be used before it is declared.

hoistedExecute(); //defined later
function hoistedExecute(){
  console.log('In hoistedExecute function');
}
//Use of variable
console.log(iAmDefinedLater); //prints undefined
var iAmDefinedLater = 'hoisted';
//Not defining iAmDefinedLater ever throws error

Above is possible because of hoisting. All the functions are placed at the top of the scope. And variable declared using var keyword is kept at the top leaving the assignment at the same place. e.g.

This code

anyFunction();
var aVariable = 'global';
function anyFunction() {
  console.log('anyFunction executed');
  //Error: localFunction is until now undefined
  localFunction(); //If commented
  //Would print 'anyFunction executed undefined'
  var aVariable = 'local';
  var localFunction = function(){
    console.log('localFunction executed');
  };
}

transforms to

var aVariable; //declaration shifted to top
//Full function moved to top
function anyFunction() {
  //exactly same happens inside a function too
  var aVariable;
  var localFunction;
  console.log('anyFunction executed ');
  localFunction();
  aVariable = 'local';
  localFunction = function() {
      console.log('localFunction executed ');
    }; 
}
anyFunction();
aVariable = 'global';

Variables defined with let and const are not hoisted.

console.log(definedWithLet);//Gives Error
let definedWithLet = 'let';

Variable defined with const can not be hoisted as once a value is assigned to const variables, it can not be modified or reassigned.