Skip to content

Commit

Permalink
docs(ES6ClassMocks): add clarity for module factory limitations
Browse files Browse the repository at this point in the history
- close #11862
- related to #11455
  • Loading branch information
john-u committed Feb 21, 2022
1 parent 7d4595e commit a4f125b
Show file tree
Hide file tree
Showing 8 changed files with 144 additions and 8 deletions.
19 changes: 18 additions & 1 deletion docs/Es6ClassMocks.md
Original file line number Diff line number Diff line change
Expand Up @@ -140,7 +140,11 @@ jest.mock('./sound-player', () => {
});
```

A limitation with the factory parameter is that, since calls to `jest.mock()` are hoisted to the top of the file, it's not possible to first define a variable and then use it in the factory. An exception is made for variables that start with the word 'mock'. It's up to you to guarantee that they will be initialized on time! For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration:
:::caution
Since calls to `jest.mock()` are hoisted to the top of the file, Jest prevents access to out-of-scope variables. By default, you cannot first define a variable and then use it in the factory. Jest will disable this check for variables that start with the word 'mock'. However, it is still up to you to guarantee that they will be initialized on time. Be aware of [Temporal Dead Zone](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let#temporal_dead_zone_tdz).
:::

For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration.

```javascript
// Note: this will fail
Expand All @@ -153,6 +157,19 @@ jest.mock('./sound-player', () => {
});
```

The following will throw a ReferenceError despite using 'mock' in the variable declaration, as the mockSoundPlayer is not wrapped in an arrow function and thus accessed before initialization after hoisting.

```javascript
import SoundPlayer from './sound-player';
const mockSoundPlayer = jest.fn().mockImplementation(() => {
return {playSoundFile: mockPlaySoundFile};
});
// results in a ReferenceError
jest.mock('./sound-player', () => {
return mockSoundPlayer;
});
```

### Replacing the mock using [`mockImplementation()`](MockFunctionAPI.md#mockfnmockimplementationfn) or [`mockImplementationOnce()`](MockFunctionAPI.md#mockfnmockimplementationoncefn)

You can replace all of the above mocks in order to change the implementation, for a single test or all tests, by calling `mockImplementation()` on the existing mock.
Expand Down
19 changes: 18 additions & 1 deletion website/versioned_docs/version-25.x/Es6ClassMocks.md
Original file line number Diff line number Diff line change
Expand Up @@ -140,7 +140,11 @@ jest.mock('./sound-player', () => {
});
```

A limitation with the factory parameter is that, since calls to `jest.mock()` are hoisted to the top of the file, it's not possible to first define a variable and then use it in the factory. An exception is made for variables that start with the word 'mock'. It's up to you to guarantee that they will be initialized on time! For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration:
:::caution
Since calls to `jest.mock()` are hoisted to the top of the file, Jest prevents access to out-of-scope variables. By default, you cannot first define a variable and then use it in the factory. Jest will disable this check for variables that start with the word 'mock'. However, it is still up to you to guarantee that they will be initialized on time. Be aware of [Temporal Dead Zone](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let#temporal_dead_zone_tdz).
:::

For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration.

```javascript
// Note: this will fail
Expand All @@ -153,6 +157,19 @@ jest.mock('./sound-player', () => {
});
```

The following will throw a ReferenceError despite using 'mock' in the variable declaration, as the mockSoundPlayer is not wrapped in an arrow function and thus accessed before initialization after hoisting.

```javascript
import SoundPlayer from './sound-player';
const mockSoundPlayer = jest.fn().mockImplementation(() => {
return {playSoundFile: mockPlaySoundFile};
});
// results in a ReferenceError
jest.mock('./sound-player', () => {
return mockSoundPlayer;
});
```

### Replacing the mock using [`mockImplementation()`](MockFunctionAPI.md#mockfnmockimplementationfn) or [`mockImplementationOnce()`](MockFunctionAPI.md#mockfnmockimplementationoncefn)

You can replace all of the above mocks in order to change the implementation, for a single test or all tests, by calling `mockImplementation()` on the existing mock.
Expand Down
19 changes: 18 additions & 1 deletion website/versioned_docs/version-26.x/Es6ClassMocks.md
Original file line number Diff line number Diff line change
Expand Up @@ -140,7 +140,11 @@ jest.mock('./sound-player', () => {
});
```

A limitation with the factory parameter is that, since calls to `jest.mock()` are hoisted to the top of the file, it's not possible to first define a variable and then use it in the factory. An exception is made for variables that start with the word 'mock'. It's up to you to guarantee that they will be initialized on time! For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration:
:::caution
Since calls to `jest.mock()` are hoisted to the top of the file, Jest prevents access to out-of-scope variables. By default, you cannot first define a variable and then use it in the factory. Jest will disable this check for variables that start with the word 'mock'. However, it is still up to you to guarantee that they will be initialized on time. Be aware of [Temporal Dead Zone](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let#temporal_dead_zone_tdz).
:::

For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration.

```javascript
// Note: this will fail
Expand All @@ -153,6 +157,19 @@ jest.mock('./sound-player', () => {
});
```

The following will throw a ReferenceError despite using 'mock' in the variable declaration, as the mockSoundPlayer is not wrapped in an arrow function and thus accessed before initialization after hoisting.

```javascript
import SoundPlayer from './sound-player';
const mockSoundPlayer = jest.fn().mockImplementation(() => {
return {playSoundFile: mockPlaySoundFile};
});
// results in a ReferenceError
jest.mock('./sound-player', () => {
return mockSoundPlayer;
});
```

### Replacing the mock using [`mockImplementation()`](MockFunctionAPI.md#mockfnmockimplementationfn) or [`mockImplementationOnce()`](MockFunctionAPI.md#mockfnmockimplementationoncefn)

You can replace all of the above mocks in order to change the implementation, for a single test or all tests, by calling `mockImplementation()` on the existing mock.
Expand Down
19 changes: 18 additions & 1 deletion website/versioned_docs/version-27.0/Es6ClassMocks.md
Original file line number Diff line number Diff line change
Expand Up @@ -140,7 +140,11 @@ jest.mock('./sound-player', () => {
});
```

A limitation with the factory parameter is that, since calls to `jest.mock()` are hoisted to the top of the file, it's not possible to first define a variable and then use it in the factory. An exception is made for variables that start with the word 'mock'. It's up to you to guarantee that they will be initialized on time! For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration:
:::caution
Since calls to `jest.mock()` are hoisted to the top of the file, Jest prevents access to out-of-scope variables. By default, you cannot first define a variable and then use it in the factory. Jest will disable this check for variables that start with the word 'mock'. However, it is still up to you to guarantee that they will be initialized on time. Be aware of [Temporal Dead Zone](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let#temporal_dead_zone_tdz).
:::

For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration.

```javascript
// Note: this will fail
Expand All @@ -153,6 +157,19 @@ jest.mock('./sound-player', () => {
});
```

The following will throw a ReferenceError despite using 'mock' in the variable declaration, as the mockSoundPlayer is not wrapped in an arrow function and thus accessed before initialization after hoisting.

```javascript
import SoundPlayer from './sound-player';
const mockSoundPlayer = jest.fn().mockImplementation(() => {
return {playSoundFile: mockPlaySoundFile};
});
// results in a ReferenceError
jest.mock('./sound-player', () => {
return mockSoundPlayer;
});
```

### Replacing the mock using [`mockImplementation()`](MockFunctionAPI.md#mockfnmockimplementationfn) or [`mockImplementationOnce()`](MockFunctionAPI.md#mockfnmockimplementationoncefn)

You can replace all of the above mocks in order to change the implementation, for a single test or all tests, by calling `mockImplementation()` on the existing mock.
Expand Down
19 changes: 18 additions & 1 deletion website/versioned_docs/version-27.1/Es6ClassMocks.md
Original file line number Diff line number Diff line change
Expand Up @@ -140,7 +140,11 @@ jest.mock('./sound-player', () => {
});
```

A limitation with the factory parameter is that, since calls to `jest.mock()` are hoisted to the top of the file, it's not possible to first define a variable and then use it in the factory. An exception is made for variables that start with the word 'mock'. It's up to you to guarantee that they will be initialized on time! For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration:
:::caution
Since calls to `jest.mock()` are hoisted to the top of the file, Jest prevents access to out-of-scope variables. By default, you cannot first define a variable and then use it in the factory. Jest will disable this check for variables that start with the word 'mock'. However, it is still up to you to guarantee that they will be initialized on time. Be aware of [Temporal Dead Zone](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let#temporal_dead_zone_tdz).
:::

For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration.

```javascript
// Note: this will fail
Expand All @@ -153,6 +157,19 @@ jest.mock('./sound-player', () => {
});
```

The following will throw a ReferenceError despite using 'mock' in the variable declaration, as the mockSoundPlayer is not wrapped in an arrow function and thus accessed before initialization after hoisting.

```javascript
import SoundPlayer from './sound-player';
const mockSoundPlayer = jest.fn().mockImplementation(() => {
return {playSoundFile: mockPlaySoundFile};
});
// results in a ReferenceError
jest.mock('./sound-player', () => {
return mockSoundPlayer;
});
```

### Replacing the mock using [`mockImplementation()`](MockFunctionAPI.md#mockfnmockimplementationfn) or [`mockImplementationOnce()`](MockFunctionAPI.md#mockfnmockimplementationoncefn)

You can replace all of the above mocks in order to change the implementation, for a single test or all tests, by calling `mockImplementation()` on the existing mock.
Expand Down
19 changes: 18 additions & 1 deletion website/versioned_docs/version-27.2/Es6ClassMocks.md
Original file line number Diff line number Diff line change
Expand Up @@ -140,7 +140,11 @@ jest.mock('./sound-player', () => {
});
```

A limitation with the factory parameter is that, since calls to `jest.mock()` are hoisted to the top of the file, it's not possible to first define a variable and then use it in the factory. An exception is made for variables that start with the word 'mock'. It's up to you to guarantee that they will be initialized on time! For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration:
:::caution
Since calls to `jest.mock()` are hoisted to the top of the file, Jest prevents access to out-of-scope variables. By default, you cannot first define a variable and then use it in the factory. Jest will disable this check for variables that start with the word 'mock'. However, it is still up to you to guarantee that they will be initialized on time. Be aware of [Temporal Dead Zone](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let#temporal_dead_zone_tdz).
:::

For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration.

```javascript
// Note: this will fail
Expand All @@ -153,6 +157,19 @@ jest.mock('./sound-player', () => {
});
```

The following will throw a ReferenceError despite using 'mock' in the variable declaration, as the mockSoundPlayer is not wrapped in an arrow function and thus accessed before initialization after hoisting.

```javascript
import SoundPlayer from './sound-player';
const mockSoundPlayer = jest.fn().mockImplementation(() => {
return {playSoundFile: mockPlaySoundFile};
});
// results in a ReferenceError
jest.mock('./sound-player', () => {
return mockSoundPlayer;
});
```

### Replacing the mock using [`mockImplementation()`](MockFunctionAPI.md#mockfnmockimplementationfn) or [`mockImplementationOnce()`](MockFunctionAPI.md#mockfnmockimplementationoncefn)

You can replace all of the above mocks in order to change the implementation, for a single test or all tests, by calling `mockImplementation()` on the existing mock.
Expand Down
19 changes: 18 additions & 1 deletion website/versioned_docs/version-27.4/Es6ClassMocks.md
Original file line number Diff line number Diff line change
Expand Up @@ -140,7 +140,11 @@ jest.mock('./sound-player', () => {
});
```

A limitation with the factory parameter is that, since calls to `jest.mock()` are hoisted to the top of the file, it's not possible to first define a variable and then use it in the factory. An exception is made for variables that start with the word 'mock'. It's up to you to guarantee that they will be initialized on time! For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration:
:::caution
Since calls to `jest.mock()` are hoisted to the top of the file, Jest prevents access to out-of-scope variables. By default, you cannot first define a variable and then use it in the factory. Jest will disable this check for variables that start with the word 'mock'. However, it is still up to you to guarantee that they will be initialized on time. Be aware of [Temporal Dead Zone](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let#temporal_dead_zone_tdz).
:::

For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration.

```javascript
// Note: this will fail
Expand All @@ -153,6 +157,19 @@ jest.mock('./sound-player', () => {
});
```

The following will throw a ReferenceError despite using 'mock' in the variable declaration, as the mockSoundPlayer is not wrapped in an arrow function and thus accessed before initialization after hoisting.

```javascript
import SoundPlayer from './sound-player';
const mockSoundPlayer = jest.fn().mockImplementation(() => {
return {playSoundFile: mockPlaySoundFile};
});
// results in a ReferenceError
jest.mock('./sound-player', () => {
return mockSoundPlayer;
});
```

### Replacing the mock using [`mockImplementation()`](MockFunctionAPI.md#mockfnmockimplementationfn) or [`mockImplementationOnce()`](MockFunctionAPI.md#mockfnmockimplementationoncefn)

You can replace all of the above mocks in order to change the implementation, for a single test or all tests, by calling `mockImplementation()` on the existing mock.
Expand Down
19 changes: 18 additions & 1 deletion website/versioned_docs/version-27.5/Es6ClassMocks.md
Original file line number Diff line number Diff line change
Expand Up @@ -140,7 +140,11 @@ jest.mock('./sound-player', () => {
});
```

A limitation with the factory parameter is that, since calls to `jest.mock()` are hoisted to the top of the file, it's not possible to first define a variable and then use it in the factory. An exception is made for variables that start with the word 'mock'. It's up to you to guarantee that they will be initialized on time! For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration:
:::caution
Since calls to `jest.mock()` are hoisted to the top of the file, Jest prevents access to out-of-scope variables. By default, you cannot first define a variable and then use it in the factory. Jest will disable this check for variables that start with the word 'mock'. However, it is still up to you to guarantee that they will be initialized on time. Be aware of [Temporal Dead Zone](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let#temporal_dead_zone_tdz).
:::

For example, the following will throw an out-of-scope error due to the use of 'fake' instead of 'mock' in the variable declaration.

```javascript
// Note: this will fail
Expand All @@ -153,6 +157,19 @@ jest.mock('./sound-player', () => {
});
```

The following will throw a ReferenceError despite using 'mock' in the variable declaration, as the mockSoundPlayer is not wrapped in an arrow function and thus accessed before initialization after hoisting.

```javascript
import SoundPlayer from './sound-player';
const mockSoundPlayer = jest.fn().mockImplementation(() => {
return {playSoundFile: mockPlaySoundFile};
});
// results in a ReferenceError
jest.mock('./sound-player', () => {
return mockSoundPlayer;
});
```

### Replacing the mock using [`mockImplementation()`](MockFunctionAPI.md#mockfnmockimplementationfn) or [`mockImplementationOnce()`](MockFunctionAPI.md#mockfnmockimplementationoncefn)

You can replace all of the above mocks in order to change the implementation, for a single test or all tests, by calling `mockImplementation()` on the existing mock.
Expand Down

0 comments on commit a4f125b

Please sign in to comment.