assertly/docs/words/key.md at master · EpiphanySoft/assertly

The key or keys assertion checks that a given set of property names ("keys") are present on the given value.

For example:

let o = { a: 1 };

expect(o).to.have.key('a');

You can check for multiple keys as well:

let o = { a: 1, b: 2 };

expect(o).to.have.keys('a', 'b');

You can combined this with own to filter out inherited properties:

let a = { a: 1 };
let b = Object.create(a);

expect(b).to.have.own.key('a');  // fails because "a" is inherited

The only modifier is also useful to ensure that no other keys are present.

For example:

let o = { a: 1, b: 2 };

expect(o).to.only.have.key('a');  // fails because "b" is also present

Of course these can be combined:

let a = { a: 1 };
let b = Object.create(a);

b.b = 2;

expect(b).to.have.only.own.key('b');

This assertion succeeds because, while "b" inherits the "a" property, "b" is the only "own" property (as defined by hasOwnProperty).

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