partial function Null safety

A matcher for maps that only checks the values of the provided keys.

This matcher only matches the keys from map. Other keys in the actual map are ignored, and any value will be accepted.

Example:

    var map = {
      "id": 1,
      "name": "foo"
    };

    expect(map, partial({
      "id": isInteger
    })); // succeeds

You may enforce that the actual value does not have a key by storing isNotPresent for that key.

Example:

  var map = {
    "id": 1,
    "name": "foo"
  };

  expect(map, partial({
    "id": isInteger,
    "name": isNotPresent
  })); // fails because 'name' is present