JSFiddle - React, Tailwind, and code Playground

JavaScript

var obj = {1234: "Martin", 4567: "Alf", 8512: "Symon"};

var find = function(input, target){
  var found;
  for (var prop in input) {
    if(input[prop] == target){
        found = prop;
    }
  };
  
  return found;
};

var found = find(obj, 'Alf');

if(found){
	alert(found);
}