Declaring variables in JS

Three possible declaration (const, let, var) 
const a = 3;
let b = 2;
var c = 1;
Re-assignment 
const a = 3;
let b = 2;
var c = 1;

// a = 4; error a cannot be re-assigned
b = 3; //OK
c = 4; //OK
Bloc scope VS function scope 
function someFunction() {
 if( someCondition ) {
   const a = 3;
   let b = 2;
   var c = 1;
 } // a and b are deleted

  // console.log(a); error a doesn't exist
  // console.log(b); error b doesn't exist
  console.log(c); // OK, c exists within the 
  // entire function
}