JSFiddle - React, Tailwind, and code Playground

JavaScript

function test(expressionFn) {
  var expression = getExpression(expressionFn);
  // get value expression.expressionRight in scope
  // not work -> var valueRigthInScope = expressionFn.prototype.constructor[[[Scopes]]][expression.expressionRight];
  console.log(expressionFn.prototype); // see ".constructor[[[Scopes]]]" in debug tools [F12]
}

function getExpression(expressionFn) {
  var strAfterReturn = expressionFn.toString().split("return")[1].trim();
  let strExpression = strAfterReturn.split(";")[0].split(" ");
  return {
      expressionLeft: strExpression[0],
      operator: strExpression[1],
      expressionRight: strExpression[2]
  };
}

function start(){
	var myValue = "This is value!";
	test(function(x) { return x.prop1 == myValue; });
}

start();