var is global scope, const is block scoped... <script> var x = 1; if(x < 5) { // now y is global (window.y can be accessed everywhere) // using c

var is global scope, const is block scoped... <script> var x = 1; if(x < 5) { // now y is global (window.y can be accessed everywhere) // using const y = x * 2 would be inaccessible outside the if block var y = x * 2; console.log('double x is: " + y); } </script> Besides that, var is "pulled" upwards, as if it was the first line in the function. That may have side effects.