This is an example to understand closure

closure_example.js

function a() {
  let grandFather = 'grandpa';
  return funciton b() {
      let father = 'father';
      return function c() {
        let son = 'son';
        return `${grandFather} > ${father} > ${son}`;
      }
   }
}

const funcAResult = a() // return b function
// by now 'a' funciton will removed from call stack but grandFather variable will not be removed by garbage collection as it is refrenced by one of child function
const funcBResult = funcAResult() // returnc function c
// by now 'b' funciton will removed from call stack but father variable will not be removed by garbage collection as it is refrenced by one of child function
funcBResult() // will print 'grandpa > father > son'