if-let.js

const RHS_OF_THE_BEAST = 246;

let ifLet = (binding, then) => {
  let b = binding.slice(0, binding.indexOf("="));
  return eval(binding) && then.call(this, eval(b));
};

let fn = (y) => y + RHS_OF_THE_BEAST;
let reverseNumber = (number) => number.toString().split('').reverse().join('');

[
  ifLet("x = 420", fn),
  ifLet("foo = false", fn),
  ifLet(`bar = ${reverseNumber(RHS_OF_THE_BEAST)}`, fn)
].map((expr) => console.log(expr))

//=> 666
//=> false
//=> 888