Unified object assignment

assign.js

const assign = (target, key, value) =>                                                                                                                                                   
  Object.assign(target, Object(key) === key ? key : {[key]: value});

// Example

const object = assign({
  foo: 1
}, "bar", 2);

assign(object, {
  "baz": 3
});

console.log(object); // {foo: 1, bar: 2, baz: 3}