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69 lines
3.3 KiB
Text
69 lines
3.3 KiB
Text
---
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sidebar_position: 2
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slug: /api/misc/@docusaurus/logger
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---
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# 📦 logger
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An encapsulated logger for semantically formatting console messages.
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Authors of packages in the Docusaurus ecosystem are encouraged to use this package to provide unified log formats.
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## APIs
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It exports a single object as default export: `logger`. `logger` has the following properties:
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- Some useful colors.
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- `red`
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- `yellow`
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- `green`
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- `bold`
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- `dim`
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- Formatters. These functions all have the signature `(msg: unknown) => string`. Note that their implementations are not guaranteed. You should only care about their semantics.
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- `path`: formats a file path.
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- `url`: formats a URL.
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- `name`: formats an identifier.
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- `code`: formats a code snippet.
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- `subdue`: subdues the text.
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- `num`: formats a number.
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- The `interpolate` function. It is a template literal tag. The syntax can be found below.
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- Logging functions. All logging functions can both be used as normal functions (similar to the `console.log` family, but only accepts one parameter) or template literal tags.
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- `info`: prints information.
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- `warn`: prints a warning that should be paid attention to.
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- `error`: prints an error (not necessarily halting the program) that signals significant problems.
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- `success`: prints a success message.
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- The `report` function. It takes a `ReportingSeverity` value (`ignore`, `log`, `warn`, `throw`) and reports a message according to the severity.
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:::warning A word on the `error` formatter
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Beware that an `error` message, even when it doesn't hang the program, is likely going to cause confusion. When users inspect logs and find an `[ERROR]`, even when the build succeeds, they will assume something is going wrong. Use it sparingly.
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Docusaurus only uses `logger.error` when printing messages immediately before throwing an error, or when user has set the reporting severity of `onBrokenLink`, etc. to `"error"`.
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In addition, `warn` and `error` will color the **entire** message for better attention. If you are printing large blocks of help text about an error, better use `logger.info`.
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:::
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### Using the template literal tag
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The template literal tag evaluates the template and expressions embedded. `interpolate` returns a new string, while other logging functions prints it. Below is a typical usage:
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```js
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logger.info`Hello name=${name}! You have number=${money} dollars. Here are the ${
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items.length > 1 ? 'items' : 'item'
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} on the shelf: ${items}
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To buy anything, enter code=${'buy x'} where code=${'x'} is the item's name; to quit, press code=${'Ctrl + C'}.`;
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```
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An embedded expression is optionally preceded by a flag in the form `[a-z]+=` (a few lowercase letters, followed by an equals sign, directly preceding the embedded expression). If the expression is not preceded by any flag, it's printed out as-is. Otherwise, it's formatted with one of the formatters:
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- `path=`: `path`
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- `url=`: `url`
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- `name=`: `name`
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- `code=`: `code`
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- `subdue=`: `subdue`
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- `number=`: `num`
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If the expression is an array, it's formatted by `` `\n- ${array.join('\n- ')}\n` `` (note it automatically gets a leading line end). Each member is formatted by itself and the bullet is not formatted. So you would see the above message printed as:
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