Astring

A tiny and fast JavaScript code generator from an ESTree-formatted AST.

Key features:

• Supports ECMAScript versions 5 and 6.
• Works both in a browser and in Node.
• Considerably faster than Escodegen.
• Smaller than Esotope and faster for small ASTs.
• No dependencies and small footprint (12 KB minified, 3 KB gziped).
• Output code is readable and executable.
• Reduced formatting options.

Installation

The easiest way is to install it with the Node Package Manager:

npm install astring

Alternatively, checkout this repository and install the development dependencies:

git clone https://github.com/davidbonnet/astring.git
cd astring
npm install

The path to the module file is dist/astring.min.js and can be linked to from an HTML webpage. When used in a browser environment, the module exposes a global variable astring:

<script src="astring.min.js" type="text/javascript"></script>

Usage

The astring module consists of a function that takes two arguments: node and options. It returns a string representing the rendered code of the provided AST node. The options are:

• indent: string to use for indentation (defaults to "\t")
• lineEnd: string to use for line endings (defaults to "\n")
• startingIndentLevel: indent level to start from (defaults to 0)

Example

This example uses Acorn, a blazingly fast JavaScript parser and AST producer. It is the perfect companion of Astring.

// Import modules (unecessary when run in a browser)
acorn = require( 'acorn' );
astring = require( 'astring' );

// Example code
var code = "let answer = 4 + 7 * 5 + 3;\n";

// Parse it into an AST
var ast = acorn.parse( code, { ecmaVersion: 6 } );

// Set formatting options
var options = {
    indent: '   ',
    lineEnd: '\n'
};

// Format it
var result = astring( ast, options );

// Check it
if ( code === result ) {
    console.log( 'It works !' );
} else {
    console.log( 'Something went wrong…' );
}

Command line interface

The bin/astring utility can be used to convert a JSON-formatted ESTree compliant AST of a JavaScript code. It accepts the following arguments:

• --indent: string to use as indentation (defaults to "\t")
• --lineEnd: string to use for line endings (defaults to "\n")
• --startingIndentLevel: indent level to start from (defaults to 0)

The utility reads the AST from stdin or from a provided list of files, and prints out the resulting code.

Example

As in the previous example, we use Acorn to get the JSON-formatted AST. This command pipes the AST output by acorn to astring in order to obtain the formatted JavaScript code:

acorn --ecma6 script.js | astring --indent "  " > result.js

This command does the same, but reads the AST from an intermediary file:

acorn --ecma6 script.js > ast.json
astring --indent "  " ast.json > result.js

Benchmark

From the repository, you can run benchmarks that compare Astring against Escodegen and Esotope:

npm run benchmark

TODO

• Comments generation (version 0.3.x)
• More tests (patches)