Difference between “var” and “let” Keywords?

Answer:

In javascript, var and let both are used for variable declaration but the difference between them is that var has function level scope and let has block level scope.
var was there from the beginning but, let was introduced in ES2015/ES6.

Input:

// calling var x after definition
var x = 19;
document.write(x, "\n");

// calling var z before definition will return undefined
document.write(z, "\n");
var z = 23;

// calling let y after definition
let y = 15;
document.write(y, "\n");

// calling let a before definition will give error
document.write(a);
let a = 6;


Output:

19 undefined 15 error