Converting lodash _.uniqBy() to native javascript

Question

Here in this snippet i am stuck as in _.uniqBy(array,iteratee),this

• iteratee can be a function or a string at the same time

Answer 1

I'm running my code through Webpack via CreateReactApp, it must be using a polyfill for spread that uses slice. Here's what I did instead, a variation of @oridori's answer:

const uniqBy = (arr: any[], predicate: (item: any) => string) => {
  const cb = typeof predicate === 'function' ? predicate : (o) => o[predicate];
  const result = [];
  const map = new Map();

  arr.forEach((item) => {
    const key = (item === null || item === undefined) ? item : cb(item);

    if (!map.has(key)) {
      map.set(key, item);
      result.push(item);
    }
  });

  return result;
};