What does flatten a nested object do code example

Example 1: make a flat object from object of object list

var object =  { 0: [1, 2, 3, 4] },
    result = Object.keys(object).reduce(function (r, k) {
        return r.concat(k, object[k]);
    }, []);
    
console.log(result);

Example 2: flatten nested object js

Object.assign(
  {}, 
  ...function _flatten(o) { 
    return [].concat(...Object.keys(o)
      .map(k => 
        typeof o[k] === 'object' ?
          _flatten(o[k]) : 
          ({[k]: o[k]})
      )
    );
  }(yourObject)
)