Code formatter

Deno ships with a built in code formatter that will auto-format the following files:

File Type Extension
JavaScript .js
TypeScript .ts
JSX .jsx
TSX .tsx
Markdown .md, .markdown
JSON .json
JSONC .jsonc

as well as code snippets within Markdown files.

# format all supported files in the current directory and subdirectories
deno fmt
# format specific files
deno fmt myfile1.ts myfile2.ts
# check if all the supported files in the current directory and subdirectories are formatted
deno fmt --check
# format stdin and write to stdout
cat file.ts | deno fmt -

Ignoring Code

Ignore formatting code by preceding it with a // deno-fmt-ignore comment in TS/JS/JSONC:

// deno-fmt-ignore
export const identity = [
    1, 0, 0,
    0, 1, 0,
    0, 0, 1,

Or ignore an entire file by adding a // deno-fmt-ignore-file comment at the top of the file.

In markdown you may use a <!-- deno-fmt-ignore --> comment or ignore a whole file with a <!-- deno-fmt-ignore-file --> comment. To ignore a section of markdown, surround the code with <!-- deno-fmt-ignore-start --> and <!-- deno-fmt-ignore-end --> comments.


ℹ️ It is recommended to stick with default options.

Starting with Deno v1.14 a formatter can be customized using either a configuration file or following CLI flags:

  • --options-use-tabs - Whether to use tabs. Defaults to false (using spaces).

  • --options-line-width - The width of a line the printer will try to stay under. Note that the printer may exceed this width in certain cases. Defaults to 80.

  • --options-indent-width - The number of characters for an indent. Defaults to 2.

  • --options-single-quote - Wheter to use single quote. Defaults to false (using double quote).

  • --options-prose-wrap={always,never,preserve} - Define how prose should be wrapped in Markdown files. Defaults to "always".