basic native implementation for isEqual lodash

isEqual.js

const isEqual = (first: any, second: any): boolean => {
  if (first === second) {
    return true;
  }
  if ((first === undefined || second === undefined || first === null || second === null)
    && (first || second)) {
    return false;
  }
  const firstType = first?.constructor.name;
  const secondType = second?.constructor.name;
  if (firstType !== secondType) {
    return false;
  }
  if (firstType === 'Array') {
    if (first.length !== second.length) {
      return false;
    }
    let equal = true;
    for (let i = 0; i < first.length; i++) {
      if (!isEqual(first[i], second[i])) {
        equal = false;
        break;
      }
    }
    return equal;
  }
  if (firstType === 'Object') {
    let equal = true;
    const fKeys = Object.keys(first);
    const sKeys = Object.keys(second);
    if (fKeys.length !== sKeys.length) {
      return false;
    }
    for (let i = 0; i < fKeys.length; i++) {
      if (first[fKeys[i]] && second[fKeys[i]]) {
        if (first[fKeys[i]] === second[fKeys[i]]) {
          continue; // eslint-disable-line
        }
        if (first[fKeys[i]] && (first[fKeys[i]].constructor.name === 'Array'
          || first[fKeys[i]].constructor.name === 'Object')) {
          equal = isEqual(first[fKeys[i]], second[fKeys[i]]);
          if (!equal) {
            break;
          }
        } else if (first[fKeys[i]] !== second[fKeys[i]]) {
          equal = false;
          break;
        }
      } else if ((first[fKeys[i]] && !second[fKeys[i]]) || (!first[fKeys[i]] && second[fKeys[i]])) {
        equal = false;
        break;
      }
    }
    return equal;
  }
  return first === second;
};

There is a syntax error in the first line:
function isEqual = (first, second) => {
It should be:
var isEqual = (first, second) => {
or
function isEqual(first, second) {

Thanks @euglv, for pointing it out I missed it while pasting it in the gist. Fixed it now.