nested_set_get.js

// Get x[path]
// Path may be nested, with dot notation, 
// e.g. get(x, 'foo.bar.baz.name') => x.foo.bar.baz.name
function get(path, x){
  checkPath(path);
  var keys = path.split('.');
  
  return keys.reduce((obj, key) => {
    return obj[key];
  }, x)
}

function set(path, val, x){
  checkPath(path);
  
  var keys = path.split('.');
  var last = keys.pop();
  
  var reduced = keys.reduce((obj, key) => {
    return obj[key];
  }, x);
  
  reduced[last] = val;
  return reduced;
}
    
function checkPath(path){
  if(typeof path !== 'string')
    throw new Error('first arg should be string');
  if(path.length === 0)
    throw new Error('first arg should contain str');
  
  return true;
}