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8.4.0 • Public • Published

Acorn loose parser

An error-tolerant JavaScript parser written in JavaScript.

This parser will parse any text into an ESTree syntax tree that is a reasonable approximation of what it might mean as a JavaScript program.

It will, to recover from missing brackets, treat whitespace as significant, which has the downside that it might mis-parse a valid but weirdly indented file. It is recommended to always try a parse with the regular acorn parser first, and only fall back to this parser when that one finds syntax errors.


Acorn is open source software released under an MIT license.

You are welcome to report bugs or create pull requests on github.


The easiest way to install acorn-loose is from npm:

npm install acorn-loose

Alternately, you can download the source and build acorn yourself:

git clone
cd acorn
npm install


parse(input, options) takes an input string and a set of options (the same options as acorn takes), and returns a syntax tree, even if the code isn't syntactically valid. It'll insert identifier nodes with name "✖" as placeholders in places where it can't make sense of the input. Depends on the acorn package, because it uses the same tokenizer.

var acornLoose = require("acorn-loose");
console.log(acornLoose.parse("1 / * 4 )[2]", {ecmaVersion: 2020}));

Like the regular parser, the loose parser supports plugins. You can take the LooseParser class exported by the module, and call its static extend method with one or more plugins to get a customized parser class. The class has a static parse method that acts like the top-level parse method.

isDummy(node) takes a Node and returns true if it is a dummy node inserted by the parser. The function performs a simple equality check on the node's name.




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  • marijn
  • adrianheine
  • rreverser