Iterating Over Object Entries in JS using for...in | Performance Comparison [https://gists.cwidanage.com/2018/06/how-to-iterate-over-object-entries-in.html]

for_in.js

let obj = {
  key1: "value1",
  key2: "value2",
  key3: "value3"
}

for (const key in obj) {
  let value = obj[key];
  
  //optional check for properties from prototype chain
  if (obj.hasOwnProperty(key)) {
    //no a property from prototype chain     
  }else{
    //property from protytpe chain
  }
}