フォーマットオプションのデフォルト設定を確認する方法
フォーマットオプションのデフォルト設定は下記ページで確認できます。

Options · Prettier
Prettier ships with a handful of format options.
バージョン2.5.1時点では下記オプションがあります(カッコ内がデフォルトの値)。
- Print Width(80)
- Tab Width(2)
- Tabs(false)
- Semicolons(true)
- Quotes(false)
- Quote Props("as-needed")
- JSX Quotes(false)
- Trailing Commas("es5")
- Bracket Spacing(true)
- Bracket Line(false)
- [Deprecated] JSX Brackets(false)
- Arrow Function Parentheses("always")
- Range(0 - Inifinity)
- Parser(None)
- File Path(None)
- Require Pragma(false)
- Insert Pragma(false)
- Prose Wrap("preserve")
- HTML Whitespace Sensitivity("css")
- Vue files script and style tags indentation(false)
- End of Line("lf")
- Embedded Language Formatting("auto")
また、--helpオプションで表示されるFormat optionsで確認することができます。
$ npx prettier --help (省略) Format options: --arrow-parens <always|avoid> Include parentheses around a sole arrow function parameter. Defaults to always. --bracket-same-line Put > of opening tags on the last line instead of on a new line. Defaults to false. --no-bracket-spacing Do not print spaces between brackets. --embedded-language-formatting <auto|off> Control how Prettier formats quoted code embedded in the file. Defaults to auto. --end-of-line <lf|crlf|cr|auto> Which end of line characters to apply. Defaults to lf. --html-whitespace-sensitivity <css|strict|ignore> How to handle whitespaces in HTML. Defaults to css. --jsx-single-quote Use single quotes in JSX. Defaults to false. --parser <flow|babel|babel-flow|babel-ts|typescript|espree|meriyah|css|less|scss|json|json5|json-stringify|graphql|markdown|mdx|vue|yaml|glimmer|html|angular|lwc> Which parser to use. --print-width The line length where Prettier will try wrap. Defaults to 80. --prose-wrap <always|never|preserve> How to wrap prose. Defaults to preserve. --quote-props <as-needed|consistent|preserve> Change when properties in objects are quoted. Defaults to as-needed. --no-semi Do not print semicolons, except at the beginning of lines which may need them. --single-quote Use single quotes instead of double quotes. Defaults to false. --tab-width Number of spaces per indentation level. Defaults to 2. --trailing-comma <es5|none|all> Print trailing commas wherever possible when multi-line. Defaults to es5. --use-tabs Indent with tabs instead of spaces. Defaults to false. --vue-indent-script-and-style Indent script and style tags in Vue files. Defaults to false. (省略)