Iterating objects https://google.github.io/styleguide/tsguide.html#iterating-objects #gogofast

1_iteratingObjects.txt

Iterating objects with for (... in ...) is error prone. It will include enumerable properties from the prototype chain. Do not use unfiltered for (... in ...) statements. Either filter values explicitly with an if statement, or use for (... of Object.keys(...)).

2_iteratingObjects.js

for (const x in someObj) {
  if (!someObj.hasOwnProperty(x)) continue;
  // now x was definitely defined on someObj
}
for (const x of Object.keys(someObj)) { // note: for _of_!
  // now x was definitely defined on someObj
}
for (const [key, value] of Object.entries(someObj)) { // note: for _of_!
  // now key was definitely defined on someObj
}