0
# Jest Console
1

2
Jest Console provides essential console utilities for the Jest testing framework, enabling developers to control and capture console output during test execution. It offers three main console implementations: BufferedConsole for collecting console output in memory, CustomConsole for providing formatted console output with custom styling, and NullConsole for completely suppressing console output during tests.
3

4
## Package Information
5

6
- **Package Name**: @jest/console
7
- **Package Type**: npm
8
- **Language**: TypeScript
9
- **Installation**: `npm install @jest/console`
10

11
## Core Imports
12

13
```typescript
14
import { BufferedConsole, CustomConsole, NullConsole, getConsoleOutput } from "@jest/console";
15
import type { ConsoleBuffer, LogMessage, LogType, LogEntry } from "@jest/console";
16
```
17

18
For CommonJS:
19

20
```javascript
21
const { BufferedConsole, CustomConsole, NullConsole, getConsoleOutput } = require("@jest/console");
22
```
23

24
## Basic Usage
25

26
```typescript
27
import { BufferedConsole, CustomConsole, NullConsole } from "@jest/console";
28

29
// BufferedConsole - capture output in memory
30
const bufferedConsole = new BufferedConsole();
31
bufferedConsole.log("Hello, World!");
32
bufferedConsole.error("Something went wrong");
33
const buffer = bufferedConsole.getBuffer();
34
// buffer contains array of log entries with messages, types, and stack traces
35

36
// CustomConsole - formatted real-time output
37
import { WriteStream } from "tty";
38
const customConsole = new CustomConsole(process.stdout, process.stderr);
39
customConsole.log("Formatted output");
40

41
// NullConsole - suppress all output
42
const nullConsole = new NullConsole();
43
nullConsole.log("This will not appear anywhere");
44
```
45

46
## Architecture
47

48
Jest Console is built around several key components:
49

50
- **BufferedConsole**: Extends Node.js Console to capture all output in memory as structured log entries
51
- **CustomConsole**: Extends Node.js Console to provide formatted output to custom streams with optional message formatting
52
- **NullConsole**: Extends CustomConsole to suppress all console output completely
53
- **Output Formatting**: Utilities for converting captured console logs into formatted, styled output strings
54

55
## Capabilities
56

57
### Buffered Console Implementation
58

59
Console implementation that captures all output in memory for later retrieval and analysis, ideal for testing scenarios where you need to verify console output.
60

61
```typescript { .api }
62
class BufferedConsole extends Console {
63
  constructor();
64
  getBuffer(): ConsoleBuffer | undefined;
65
  static write(
66
    buffer: ConsoleBuffer,
67
    type: LogType,
68
    message: LogMessage,
69
    stackLevel?: number
70
  ): ConsoleBuffer;
71
}
72
```
73

74
[BufferedConsole](./buffered-console.md)
75

76
### Custom Console Implementation
77

78
Console implementation that outputs to custom streams with optional formatting, perfect for providing styled console output in custom environments.
79

80
```typescript { .api }
81
type Formatter = (type: LogType, message: LogMessage) => string;
82

83
class CustomConsole extends Console {
84
  constructor(
85
    stdout: WriteStream,
86
    stderr: WriteStream,
87
    formatBuffer?: Formatter
88
  );
89
  getBuffer(): undefined;
90
}
91
```
92

93
[CustomConsole](./custom-console.md)
94

95
### Null Console Implementation
96

97
Console implementation that suppresses all output, useful for completely silencing console output during test execution.
98

99
```typescript { .api }
100
class NullConsole extends CustomConsole {
101
  // All console methods are no-ops
102
}
103
```
104

105
[NullConsole](./null-console.md)
106

107
### Console Output Formatting
108

109
Utility function for formatting console buffer entries into readable string output with proper styling and stack traces.
110

111
```typescript { .api }
112
function getConsoleOutput(
113
  buffer: ConsoleBuffer,
114
  config: StackTraceConfig,
115
  globalConfig: Config.GlobalConfig
116
): string;
117
```
118

119
[Output Formatting](./output-formatting.md)
120

121
## Types
122

123
```typescript { .api }
124
type LogMessage = string;
125

126
type LogType =
127
  | 'assert'
128
  | 'count'
129
  | 'debug'
130
  | 'dir'
131
  | 'dirxml'
132
  | 'error'
133
  | 'group'
134
  | 'groupCollapsed'
135
  | 'info'
136
  | 'log'
137
  | 'time'
138
  | 'warn';
139

140
interface LogEntry {
141
  message: LogMessage;
142
  origin: string;
143
  type: LogType;
144
}
145

146
type ConsoleBuffer = Array<LogEntry>;
147

148
// From Node.js util module
149
interface InspectOptions {
150
  showHidden?: boolean;
151
  depth?: number | null;
152
  colors?: boolean;
153
  customInspect?: boolean;
154
  showProxy?: boolean;
155
  maxArrayLength?: number | null;
156
  maxStringLength?: number | null;
157
  breakLength?: number;
158
  compact?: boolean | number;
159
  sorted?: boolean | ((a: string, b: string) => number);
160
  getters?: boolean | 'get' | 'set';
161
}
162

163
// From Node.js tty module  
164
interface WriteStream extends NodeJS.WriteStream {
165
  isTTY: boolean;
166
  columns: number;
167
  rows: number;
168
}
169
```