Text formatters
A text formatter is a function that formats a log record into a string. LogTape has three built-in sinks that can take a text formatter:
Of course, you can write your own sinks that take a text formatter.
Built-in text formatters
LogTape provides two built-in text formatters:
Default text formatter
defaultTextFormatter formats a log record into a string with a simple format. It renders the timestamp, the log level, the message, and the prettified values embedded in the message.
It formats log records like this:
2023-11-14 22:13:20.000 +00:00 [INF] category·subcategory: Hello, world!ANSI color formatter
This API is available since LogTape 0.5.0.
ansiColorFormatter formats a log record into a string with a simple format and ANSI colors. It renders the timestamp, the log level, the message, and the prettified values embedded in the message.
It formats log records like this:
Configuring text formatters
This API is available since LogTape 0.6.0.
You can customize the built-in text formatters with a TextFormatterOptions or an AnsiColorFormatterOptions object without building a new text formatter from scratch.
Default text formatter
You can customize the default text formatter by calling the getTextFormatter() function with a TextFormatterOptions object. Customizable options include:
timestamp
The timestamp format. This can be one of the following:
"date-time-timezone": The date and time with the full timezone offset (e.g.,2023-11-14 22:13:20.000 +00:00)."date-time-tz": The date and time with the short timezone offset (e.g.,2023-11-14 22:13:20.000 +00)."date-time": The date and time without the timezone offset (e.g.,2023-11-14 22:13:20.000)."time-timezone": The time with the full timezone offset but without the date (e.g.,22:13:20.000 +00:00)."time-tz": The time with the short timezone offset but without the date (e.g.,22:13:20.000 +00)."time": The time without the date or timezone offset (e.g.,22:13:20.000)."date": The date without the time or timezone offset (e.g.,2023-11-14)."rfc3339": The date and time in RFC 3339 format (e.g.,2023-11-14T22:13:20.000Z).
Alternatively, this can be a function that accepts a timestamp and returns a string.
The default is "date-time-timezone".
level
The log level format. This can be one of the following:
"ABBR": The log level abbreviation in uppercase (e.g.,INF)."FULL": The full log level name in uppercase (e.g.,INFO)."L": The first letter of the log level in uppercase (e.g.,I)."abbr": The log level abbreviation in lowercase (e.g.,inf)."full": The full log level name in lowercase (e.g.,info)."l": The first letter of the log level in lowercase (e.g.,i).
Alternatively, this can be a function that accepts a log level and returns a string.
The default is "ABBR".
category
The separator between the category names.
For example, if the separator is "·", the category ["a", "b", "c"] will be formatted as "a·b·c".
The default separator is "·".
If this is a function, it will be called with the category array and should return a string, which will be used for rendering the category.
value
The format of the embedded values.
A function that renders a value to a string. This function is used to render the values in the log record. The default is util.inspect() in Node.js/Bun and Deno.inspect() in Deno.
format
How those formatted parts are concatenated.
A function that formats the log record. This function is called with the formatted values and should return a string. Note that the formatted should not include a newline character at the end.
By default, this is a function that formats the log record as follows:
2023-11-14 22:13:20.000 +00:00 [INF] category·subcategory: Hello, world!ANSI color formatter
You can customize the ansiColorFormatter by calling the getAnsiColorFormatter() function with an AnsiColorFormatterOptions object. Customizable options include:
timestamp
The timestamp format. The available options are the same as the timestamp option of the default text formatter.
The default is "date-time-tz".
timestampStyle
The ANSI style for the timestamp. "dim" is used by default.
timestampColor
The ANSI color for the timestamp. No color is used by default.
level
The log level format. The available options are the same as the level option of the default text formatter.
The default is "ABBR".
levelStyle
The ANSI style for the log level. "bold" is used by default.
levelColors
The ANSI colors for the log levels. The default colors are as follows:
"debug":"blue""info":"green""warning":"yellow""error":"red""fatal":"magenta"
category
The separator between the category names. Behaves the same as the category option of the default text formatter.
The default separator is "·".
categoryStyle
The ANSI style for the category. "dim" is used by default.
categoryColor
The ANSI color for the category. No color is used by default.
value
The format of the embedded values. Behaves the same as the value option of the default text formatter.
format
How those formatted parts are concatenated. Behaves the same as the format option of the default text formatter.
Text styles
The timestampStyle, levelStyle, and categoryStyle options can be one of the following:
"bold""dim""italic""underline""strikethrough"null(no style)
Colors
The timestampColor, levelColors (an object with log levels as keys), and categoryColor options can be one of the following:
"black""red""green""yellow""blue""magenta""cyan""white"null(no color)
Fully customized text formatter
A text formatter is just a function that takes a log record and returns a string. The type of a text formatter is TextFormatter:
export type TextFormatter = (record: LogRecord) => string;If you want to build a text formatter from scratch, you can just write a function that takes a log record and returns a string. For example, the following function is a text formatter that formats log records into JSON Lines:
function jsonLinesFormatter(record: LogRecord): string {
return JSON.stringify(record) + "\n";
}