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Pretty Fast

Pretty Fast is a source-map-generating JavaScript pretty printer, that is pretty fast.

Build Status


npm install pretty-fast


var prettyFast = require("pretty-fast");

var uglyJS = "function ugly(){code()}";

var pretty = prettyFast(uglyJS, {
  url: "test.js",
  indent: "  "

// function ugly() {
//   code()
// }

// [object SourceMapGenerator]

(See the mozilla/source-map library for information on SourceMapGenerator instances, and source maps in general.)


  • url - The URL of the JavaScript source being prettified. Used in the generated source map. If you are prettifying JS that isn't from a file or doesn't have a URL, you can use a dummy value, such as "(anonymous)".

  • indent - The string that you want your code indented by. Most people want one of " ", " ", or "\t".


Please use Bugzilla


  • To be pretty fast, while still generating source maps.

  • To avoid fully parsing the source text; we should be able to get away with only a tokenizer and some heuristics.

  • Preserve comments.

  • Pretty Fast should be able to run inside Web Workers.


  • Extreme configurability of types of indentation, where curly braces go, etc.

  • To be the very fastest pretty printer in the universe. This goal is unattainable given that generating source maps is a requirement. We just need to be Pretty Fast.

  • To perfectly pretty print exactly as you would have written the code. This falls out from both not wanting to support extreme configurability, and avoiding full on parsing. We just aim to pretty print Pretty Well.