Sometimes in React you need a unique `key` to represent an object's identity. Instead of generating an id when you fetch it from an API or generating an id on the fly or using indexes (both will lead to bugs), you can use this which gives you a stable, unique id for an object. Demo: https://codesandbox.io/s/nice-gauss-h424o. Demo with React: htt…

idObj.ts

let map = new WeakMap(); // weakly holds all object refs (works in IE11+)
let n = 0; // global counter for ids

export function idObj(obj: any) {
  if (map.has(obj)) {
    return map.get(obj);
  } else {
    let key = String(++n);
    map.set(obj, key);
    return key;
  }
}

// test it out ...
let o1 = {};
let o2 = {};

console.log(idObj(o1)); // 1
console.log(idObj(o2)); // 2
console.log(idObj(o1)); // 1
o1 = { a: 1 }; // re-assign it
o2.b = 13; // mutate this one
console.log(idObj(o1)); // 3 (because 1 is gone now)
console.log(idObj(o2)); // 2 (still the same object identity)

this actually is usually a bad idea, don't do it 😅