Javascript : Var and Let

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var	let
The scope of a variable defined with var is function scope or Declared outside any function, global.	The scope of a variable defined with let is block scope.
Examples
function varandlet() { var i = 5; } console.log(i); VM131:1 Uncaught ReferenceError: i is not defined at	function varandlet() { let i = 5; } console.log(i); VM131:1 Uncaught ReferenceError: i is not defined at
function varandlet() { For(var i=0;i<10 br="" i=""> console.log(i); } Varandlet(); // Output = 10; No error here	function varandlet() { For(let i=0;i<10 br="" i=""> console.log(i); } Varandlet(); VM350:1 Uncaught ReferenceError: i is not defined at varandlet (:1:62) at :1:1 ******** LET has block level scope.
{ var o = p = 10; } console.log( o); console.log( p); // Output // O = 10 // P = 10	{ let o = p = 10; } console.log( o); console.log( p); // Output // Error O is not defined // P = 10 // In this case P becomes global variable
for (var i = 0; i < 5; ++i) { setTimeout(function () { console.log(i); // output '5' 5 times }, 100); } //Output will be five times 5 The settimeout function works in asynchronous way.	Closure in Loop for (let i = 0; i < 5; ++i) { SetTimeout(function () { console.log(i); // output '5' 5 times }, 100); } //Output will be five times 1 2 3 4 5 let in the loop can re-binds it to each iteration of the loop, making sure to re-assign t the value from the end of the previous loop iteration, so it can be used to avoid issue with closures.