Consider the following two objects:

```
const source = {
  foo: 'value',
  bar: 'value',
  baz: 'value'
};

const pattern = {
  foo: '',
  bar: ''
};

_.fn(source, pattern); // { foo: 'value', bar: 'value' }

```

In this example 'baz' property is deleted because it doesn't exist in the pattern.