JSFiddle - React, Tailwind, and code Playground

JavaScript

function outer (callback) {
      var a = 1, b = 2, c = 3;

      function getVar(varName) {
          return eval(varName);
      }      
      callback(getVar);
    }


    outer(function(getVar) {
        console.log(getVar("a"), getVar("b"), getVar("c") );
    });