how to use a value to call a var of that name in javascript code example

Example 1: js variables

// let & var are both editable variables:
var cow = 'moo';
let pig = 'oink';
cow = 10;
pig = 10;
// const is a permanent variable; you cannot change it.
const uncuttableGrass = '\/\/';
uncuttableGrass = '___';
// above throws an error

Example 2: javascript variables

// Also let, const
var e_number = 0;
var e_string = '';
var e_true = true;
var e_false = false;
var e_undefined = undefined;