Interface MatchersFunctions

Compares value with expected by calling Object.is. This method compares objects by reference instead of their contents, similarly to the strict equality operator ===.

Usage

const value = { prop: 1 };
expect(value).toBe(value);
expect(value).not.toBe({});
expect(value.prop).toBe(1);
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Compares floating point numbers for approximate equality. Use this method instead of expect(value).toBe(expected) when comparing floating point numbers.

Usage

expect(0.1 + 0.2).not.toBe(0.3);
expect(0.1 + 0.2).toBeCloseTo(0.3, 5);
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Ensures that value is not undefined.

Usage

const value = null;
expect(value).toBeDefined();
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Ensures that value is false in a boolean context, one of false, 0, '', null, undefined or NaN. Use this method when you don't care about the specific value.

Usage

const value = null;
expect(value).toBeFalsy();
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Ensures that value > expected for number or big integer values.

Usage

const value = 42;
expect(value).toBeGreaterThan(1);
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Ensures that value >= expected for number or big integer values.

Usage

const value = 42;
expect(value).toBeGreaterThanOrEqual(42);
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Ensures that value is an instance of a class. Uses instanceof operator.

Usage

expect(page).toBeInstanceOf(Page);

class Example {}
expect(new Example()).toBeInstanceOf(Example);
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Ensures that value < expected for number or big integer values.

Usage

const value = 42;
expect(value).toBeLessThan(100);
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Ensures that value <= expected for number or big integer values.

Usage

const value = 42;
expect(value).toBeLessThanOrEqual(42);
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Ensures that value is NaN.

Usage

const value = NaN;
expect(value).toBeNaN();
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Ensures that value is null.

Usage

const value = null;
expect(value).toBeNull();
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Ensures that value is true in a boolean context, anything but false, 0, '', null, undefined or NaN. Use this method when you don't care about the specific value.

Usage

const value = { example: 'value' };
expect(value).toBeTruthy();
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Ensures that value is undefined.

Usage

const value = undefined;
expect(value).toBeUndefined();
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Ensures that value is an Array or Set and contains an item equal to the expected.

For objects, this method recursively checks equality of all fields, rather than comparing objects by reference as performed by expect(value).toContain(expected).

For primitive values, this method is equivalent to expect(value).toContain(expected).

Usage

const value = [
  { example: 1 },
  { another: 2 },
  { more: 3 },
];
expect(value).toContainEqual({ another: 2 });
expect(new Set(value)).toContainEqual({ another: 2 });
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Compares contents of the value with contents of expected, performing "deep equality" check.

For objects, this method recursively checks equality of all fields, rather than comparing objects by reference as performed by expect(value).toBe(expected).

For primitive values, this method is equivalent to expect(value).toBe(expected).

Usage

const value = { prop: 1 };
expect(value).toEqual({ prop: 1 });
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Non-strict equality

expect(value).toEqual(expected) performs deep equality check that compares contents of the received and expected values. To ensure two objects reference the same instance, use expect(value).toBe(expected) instead.

expect(value).toEqual(expected) ignores undefined properties and array items, and does not insist on object types being equal. For stricter matching, use expect(value).toStrictEqual(expected).

Pattern matching

expect(value).toEqual(expected) can be also used to perform pattern matching on objects, arrays and primitive types, with the help of the following matchers:

• expect(value).any(constructor)
• expect(value).anything()
• expect(value).arrayContaining(expected)
• expect(value).closeTo(expected[, numDigits])
• expect(value).objectContaining(expected)
• expect(value).stringContaining(expected)
• expect(value).stringMatching(expected)

Here is an example that asserts some of the values inside a complex object:

expect({
  list: [1, 2, 3],
  obj: { prop: 'Hello world!', another: 'some other value' },
  extra: 'extra',
}).toEqual(expect.objectContaining({
  list: expect.arrayContaining([2, 3]),
  obj: expect.objectContaining({ prop: expect.stringContaining('Hello') }),
}));
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Ensures that value has a .length property equal to expected. Useful for arrays and strings.

Usage

expect('Hello, World').toHaveLength(12);
expect([1, 2, 3]).toHaveLength(3);
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Ensures that property at provided keyPath exists on the object and optionally checks that property is equal to the expected. Equality is checked recursively, similarly to expect(value).toEqual(expected).

Usage

const value = {
  a: {
    b: [42],
  },
  c: true,
};
expect(value).toHaveProperty('a.b');
expect(value).toHaveProperty('a.b', [42]);
expect(value).toHaveProperty('a.b[0]', 42);
expect(value).toHaveProperty('c');
expect(value).toHaveProperty('c', true);
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Ensures that string value matches a regular expression.

Usage

const value = 'Is 42 enough?';
expect(value).toMatch(/Is \d+ enough/);
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Compares contents of the value with contents of expected, performing "deep equality" check. Allows extra properties to be present in the value, unlike expect(value).toEqual(expected), so you can check just a subset of object properties.

When comparing arrays, the number of items must match, and each item is checked recursively.

Usage

const value = {
  a: 1,
  b: 2,
  c: true,
};
expect(value).toMatchObject({ a: 1, c: true });
expect(value).toMatchObject({ b: 2, c: true });

expect([{ a: 1, b: 2 }]).toMatchObject([{ a: 1 }]);
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Compares contents of the value with contents of expected and their types.

Differences from expect(value).toEqual(expected):

• Keys with undefined properties are checked. For example, { a: undefined, b: 2 } does not match { b: 2 }.
• Array sparseness is checked. For example, [, 1] does not match [undefined, 1].
• Object types are checked to be equal. For example, a class instance with fields a and b will not equal a literal object with fields a and b.

Usage

const value = { prop: 1 };
expect(value).toStrictEqual({ prop: 1 });
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Calls the function and ensures it throws an error.

Optionally compares the error with expected. Allowed expected values:

• Regular expression - error message should match the pattern.
• String - error message should include the substring.
• Error object - error message should be equal to the message property of the object.
• Error class - error object should be an instance of the class.

Usage

expect(() => {
  throw new Error('Something bad');
}).toThrow();

expect(() => {
  throw new Error('Something bad');
}).toThrow(/something/);

expect(() => {
  throw new Error('Something bad');
}).toThrow(Error);
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An alias for expect(value).toThrow([expected]).

Usage

expect(() => {
  throw new Error('Something bad');
}).toThrowError();
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